diff --git a/src/main/c/build/linux-x86_64.sh b/src/main/c/build/linux-x86_64.sh
index 8604fe7..e1b369e 100755
--- a/src/main/c/build/linux-x86_64.sh
+++ b/src/main/c/build/linux-x86_64.sh
@@ -9,9 +9,8 @@ set -e
 OS="linux"
 ARCH="x86_64"
 HOST="$ARCH-$OS-gnu"
-CFLAGS="-m64 -Wl,--wrap=memcpy"
+CFLAGS="-m64"
 LIBUSB_CONFIG="--disable-shared"
 USB4JAVA_LIBS="-lrt"
-USB4JAVA_CFLAGS="-DWRAP_MEMCPY"
 
 build
diff --git a/src/main/c/configure.ac b/src/main/c/configure.ac
index 557863c..1721999 100644
--- a/src/main/c/configure.ac
+++ b/src/main/c/configure.ac
@@ -1,12 +1,14 @@
 AC_PREREQ([2.61])
 AC_INIT([libusb4java], [1.0.0], [k@ailis.de])
 AM_INIT_AUTOMAKE([foreign -Wall -Werror -Wno-extra-portability])
+AM_SILENT_RULES(yes)
 AC_CONFIG_MACRO_DIR([m4])
 AC_CONFIG_HEADERS([config.h])
 AC_CONFIG_SRCDIR([src/usb4java.h])
 
 AC_LANG_C
 AC_PROG_CC
+AC_PROG_CC_STDC
 AM_PROG_LIBTOOL
 AC_CHECK_JAVA
 AC_CHECK_SIZEOF([void *])
diff --git a/src/main/c/src/ConfigDescriptor.c b/src/main/c/src/ConfigDescriptor.c
index aa23a84..c95059f 100644
--- a/src/main/c/src/ConfigDescriptor.c
+++ b/src/main/c/src/ConfigDescriptor.c
@@ -35,7 +35,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(ConfigDescriptor, bLength)
     struct libusb_config_descriptor *config = unwrapConfigDescriptor(env, this);
     if (!config) return 0;
 
-    return config->bLength;
+    return (jbyte) config->bLength;
 }
 
 /**
@@ -49,7 +49,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(ConfigDescriptor, bDescriptorType)
     struct libusb_config_descriptor *config = unwrapConfigDescriptor(env, this);
     if (!config) return 0;
 
-    return config->bDescriptorType;
+    return (jbyte) config->bDescriptorType;
 }
 
 /**
@@ -63,7 +63,7 @@ JNIEXPORT jshort JNICALL METHOD_NAME(ConfigDescriptor, wTotalLength)
     struct libusb_config_descriptor *config = unwrapConfigDescriptor(env, this);
     if (!config) return 0;
 
-    return config->wTotalLength;
+    return (jshort) config->wTotalLength;
 }
 
 /**
@@ -77,7 +77,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(ConfigDescriptor, bNumInterfaces)
     struct libusb_config_descriptor *config = unwrapConfigDescriptor(env, this);
     if (!config) return 0;
 
-    return config->bNumInterfaces;
+    return (jbyte) config->bNumInterfaces;
 }
 
 /**
@@ -91,7 +91,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(ConfigDescriptor, bConfigurationValue)
     struct libusb_config_descriptor *config = unwrapConfigDescriptor(env, this);
     if (!config) return 0;
 
-    return config->bConfigurationValue;
+    return (jbyte) config->bConfigurationValue;
 }
 
 /**
@@ -105,7 +105,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(ConfigDescriptor, iConfiguration)
     struct libusb_config_descriptor *config = unwrapConfigDescriptor(env, this);
     if (!config) return 0;
 
-    return config->iConfiguration;
+    return (jbyte) config->iConfiguration;
 }
 
 /**
@@ -119,7 +119,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(ConfigDescriptor, bmAttributes)
     struct libusb_config_descriptor *config = unwrapConfigDescriptor(env, this);
     if (!config) return 0;
 
-    return config->bmAttributes;
+    return (jbyte) config->bmAttributes;
 }
 
 /**
@@ -133,7 +133,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(ConfigDescriptor, bMaxPower)
     struct libusb_config_descriptor *config = unwrapConfigDescriptor(env, this);
     if (!config) return 0;
 
-    return config->MaxPower;
+    return (jbyte) config->MaxPower;
 }
 
 /**
diff --git a/src/main/c/src/DeviceDescriptor.c b/src/main/c/src/DeviceDescriptor.c
index 7200052..eb1e1df 100644
--- a/src/main/c/src/DeviceDescriptor.c
+++ b/src/main/c/src/DeviceDescriptor.c
@@ -34,7 +34,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(DeviceDescriptor, bLength)
     struct libusb_device_descriptor *device = unwrapDeviceDescriptor(env, this);
     if (!device) return 0;
 
-    return device->bLength;
+    return (jbyte) device->bLength;
 }
 
 /**
@@ -48,7 +48,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(DeviceDescriptor, bDescriptorType)
     struct libusb_device_descriptor *device = unwrapDeviceDescriptor(env, this);
     if (!device) return 0;
 
-    return device->bDescriptorType;
+    return (jbyte) device->bDescriptorType;
 }
 
 /**
@@ -62,7 +62,7 @@ JNIEXPORT jshort JNICALL METHOD_NAME(DeviceDescriptor, bcdUSB)
     struct libusb_device_descriptor *device = unwrapDeviceDescriptor(env, this);
     if (!device) return 0;
 
-    return device->bcdUSB;
+    return (jshort) device->bcdUSB;
 }
 
 /**
@@ -76,7 +76,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(DeviceDescriptor, bDeviceClass)
     struct libusb_device_descriptor *device = unwrapDeviceDescriptor(env, this);
     if (!device) return 0;
 
-    return device->bDeviceClass;
+    return (jbyte) device->bDeviceClass;
 }
 
 /**
@@ -90,7 +90,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(DeviceDescriptor, bDeviceSubClass)
     struct libusb_device_descriptor *device = unwrapDeviceDescriptor(env, this);
     if (!device) return 0;
 
-    return device->bDeviceSubClass;
+    return (jbyte) device->bDeviceSubClass;
 }
 
 /**
@@ -104,7 +104,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(DeviceDescriptor, bDeviceProtocol)
     struct libusb_device_descriptor *device = unwrapDeviceDescriptor(env, this);
     if (!device) return 0;
 
-    return device->bDeviceProtocol;
+    return (jbyte) device->bDeviceProtocol;
 }
 
 /**
@@ -118,7 +118,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(DeviceDescriptor, bMaxPacketSize0)
     struct libusb_device_descriptor *device = unwrapDeviceDescriptor(env, this);
     if (!device) return 0;
 
-    return device->bMaxPacketSize0;
+    return (jbyte) device->bMaxPacketSize0;
 }
 
 /**
@@ -132,7 +132,7 @@ JNIEXPORT jshort JNICALL METHOD_NAME(DeviceDescriptor, idVendor)
     struct libusb_device_descriptor *device = unwrapDeviceDescriptor(env, this);
     if (!device) return 0;
 
-    return device->idVendor;
+    return (jshort) device->idVendor;
 }
 
 /**
@@ -146,7 +146,7 @@ JNIEXPORT jshort JNICALL METHOD_NAME(DeviceDescriptor, idProduct)
     struct libusb_device_descriptor *device = unwrapDeviceDescriptor(env, this);
     if (!device) return 0;
 
-    return device->idProduct;
+    return (jshort) device->idProduct;
 }
 
 /**
@@ -160,7 +160,7 @@ JNIEXPORT jshort JNICALL METHOD_NAME(DeviceDescriptor, bcdDevice)
     struct libusb_device_descriptor *device = unwrapDeviceDescriptor(env, this);
     if (!device) return 0;
 
-    return device->bcdDevice;
+    return (jshort) device->bcdDevice;
 }
 
 
@@ -175,7 +175,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(DeviceDescriptor, iManufacturer)
     struct libusb_device_descriptor *device = unwrapDeviceDescriptor(env, this);
     if (!device) return 0;
 
-    return device->iManufacturer;
+    return (jbyte) device->iManufacturer;
 }
 
 /**
@@ -189,7 +189,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(DeviceDescriptor, iProduct)
     struct libusb_device_descriptor *device = unwrapDeviceDescriptor(env, this);
     if (!device) return 0;
 
-    return device->iProduct;
+    return (jbyte) device->iProduct;
 }
 
 /**
@@ -201,7 +201,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(DeviceDescriptor, iSerialNumber)
     struct libusb_device_descriptor *device = unwrapDeviceDescriptor(env, this);
     if (!device) return 0;
 
-    return device->iSerialNumber;
+    return (jbyte) device->iSerialNumber;
 }
 
 /**
@@ -215,5 +215,5 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(DeviceDescriptor, bNumConfigurations)
     struct libusb_device_descriptor *device = unwrapDeviceDescriptor(env, this);
     if (!device) return 0;
 
-    return device->bNumConfigurations;
+    return (jbyte) device->bNumConfigurations;
 }
diff --git a/src/main/c/src/DeviceList.c b/src/main/c/src/DeviceList.c
index 4247b65..cdbfe56 100644
--- a/src/main/c/src/DeviceList.c
+++ b/src/main/c/src/DeviceList.c
@@ -6,7 +6,7 @@
 #include "DeviceList.h"
 #include "Device.h"
 
-void setDeviceList(JNIEnv* env, libusb_device* const * list, int size, jobject object)
+void setDeviceList(JNIEnv* env, libusb_device* const * list, jint size, jobject object)
 {
     SET_POINTER(env, list, object, "deviceListPointer");
 
diff --git a/src/main/c/src/DeviceList.h b/src/main/c/src/DeviceList.h
index 817b306..23df636 100644
--- a/src/main/c/src/DeviceList.h
+++ b/src/main/c/src/DeviceList.h
@@ -8,7 +8,7 @@
 
 #include "usb4java.h"
 
-void setDeviceList(JNIEnv*, libusb_device* const *, int, jobject);
+void setDeviceList(JNIEnv*, libusb_device* const *, jint, jobject);
 libusb_device** unwrapDeviceList(JNIEnv*, jobject);
 void resetDeviceList(JNIEnv*, jobject);
 
diff --git a/src/main/c/src/EndpointDescriptor.c b/src/main/c/src/EndpointDescriptor.c
index d95046b..7e40a56 100644
--- a/src/main/c/src/EndpointDescriptor.c
+++ b/src/main/c/src/EndpointDescriptor.c
@@ -44,7 +44,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(EndpointDescriptor, bLength)
     struct libusb_endpoint_descriptor *ep = unwrapEndpointDescriptor(env, this);
     if (!ep) return 0;
 
-    return ep->bLength;
+    return (jbyte) ep->bLength;
 }
 
 /**
@@ -58,7 +58,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(EndpointDescriptor, bDescriptorType)
     struct libusb_endpoint_descriptor *ep = unwrapEndpointDescriptor(env, this);
     if (!ep) return 0;
 
-    return ep->bDescriptorType;
+    return (jbyte) ep->bDescriptorType;
 }
 
 /**
@@ -72,7 +72,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(EndpointDescriptor, bEndpointAddress)
     struct libusb_endpoint_descriptor *ep = unwrapEndpointDescriptor(env, this);
     if (!ep) return 0;
 
-    return ep->bEndpointAddress;
+    return (jbyte) ep->bEndpointAddress;
 }
 
 /**
@@ -86,7 +86,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(EndpointDescriptor, bmAttributes)
     struct libusb_endpoint_descriptor *ep = unwrapEndpointDescriptor(env, this);
     if (!ep) return 0;
 
-    return ep->bmAttributes;
+    return (jbyte) ep->bmAttributes;
 }
 
 /**
@@ -100,7 +100,7 @@ JNIEXPORT jshort JNICALL METHOD_NAME(EndpointDescriptor, wMaxPacketSize)
     struct libusb_endpoint_descriptor *ep = unwrapEndpointDescriptor(env, this);
     if (!ep) return 0;
 
-    return ep->wMaxPacketSize;
+    return (jshort) ep->wMaxPacketSize;
 }
 
 /**
@@ -114,7 +114,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(EndpointDescriptor, bInterval)
     struct libusb_endpoint_descriptor *ep = unwrapEndpointDescriptor(env, this);
     if (!ep) return 0;
 
-    return ep->bInterval;
+    return (jbyte) ep->bInterval;
 }
 
 /**
@@ -128,7 +128,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(EndpointDescriptor, bRefresh)
     struct libusb_endpoint_descriptor *ep = unwrapEndpointDescriptor(env, this);
     if (!ep) return 0;
 
-    return ep->bRefresh;
+    return (jbyte) ep->bRefresh;
 }
 
 /**
@@ -142,7 +142,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(EndpointDescriptor, bSynchAddress)
     struct libusb_endpoint_descriptor *ep = unwrapEndpointDescriptor(env, this);
     if (!ep) return 0;
 
-    return ep->bSynchAddress;
+    return (jbyte) ep->bSynchAddress;
 }
 
 /**
diff --git a/src/main/c/src/InterfaceDescriptor.c b/src/main/c/src/InterfaceDescriptor.c
index 297b666..d2834d5 100644
--- a/src/main/c/src/InterfaceDescriptor.c
+++ b/src/main/c/src/InterfaceDescriptor.c
@@ -47,7 +47,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(InterfaceDescriptor, bLength)
         unwrapInterfaceDescriptor(env, this);
     if (!interface) return 0;
 
-    return interface->bLength;
+    return (jbyte) interface->bLength;
 }
 
 /**
@@ -62,7 +62,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(InterfaceDescriptor, bDescriptorType)
         unwrapInterfaceDescriptor(env, this);
     if (!interface) return 0;
 
-    return interface->bDescriptorType;
+    return (jbyte) interface->bDescriptorType;
 }
 
 /**
@@ -77,7 +77,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(InterfaceDescriptor, bInterfaceNumber)
         unwrapInterfaceDescriptor(env, this);
     if (!interface) return 0;
 
-    return interface->bInterfaceNumber;
+    return (jbyte) interface->bInterfaceNumber;
 }
 
 /**
@@ -92,7 +92,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(InterfaceDescriptor, bAlternateSetting)
         unwrapInterfaceDescriptor(env, this);
     if (!interface) return 0;
 
-    return interface->bAlternateSetting;
+    return (jbyte) interface->bAlternateSetting;
 }
 
 /**
@@ -107,7 +107,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(InterfaceDescriptor, bNumEndpoints)
         unwrapInterfaceDescriptor(env, this);
     if (!interface) return 0;
 
-    return interface->bNumEndpoints;
+    return (jbyte) interface->bNumEndpoints;
 }
 
 /**
@@ -122,7 +122,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(InterfaceDescriptor, bInterfaceClass)
         unwrapInterfaceDescriptor(env, this);
     if (!interface) return 0;
 
-    return interface->bInterfaceClass;
+    return (jbyte) interface->bInterfaceClass;
 }
 
 /**
@@ -137,7 +137,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(InterfaceDescriptor, bInterfaceSubClass)
         unwrapInterfaceDescriptor(env, this);
     if (!interface) return 0;
 
-    return interface->bInterfaceSubClass;
+    return (jbyte) interface->bInterfaceSubClass;
 }
 
 /**
@@ -152,7 +152,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(InterfaceDescriptor, bInterfaceProtocol)
         unwrapInterfaceDescriptor(env, this);
     if (!interface) return 0;
 
-    return interface->bInterfaceProtocol;
+    return (jbyte) interface->bInterfaceProtocol;
 }
 
 /**
@@ -167,7 +167,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(InterfaceDescriptor, iInterface)
         unwrapInterfaceDescriptor(env, this);
     if (!interface) return 0;
 
-    return interface->iInterface;
+    return (jbyte) interface->iInterface;
 }
 
 /**
diff --git a/src/main/c/src/IsoPacketDescriptor.c b/src/main/c/src/IsoPacketDescriptor.c
index aabdb08..5bd5b72 100644
--- a/src/main/c/src/IsoPacketDescriptor.c
+++ b/src/main/c/src/IsoPacketDescriptor.c
@@ -40,7 +40,7 @@ JNIEXPORT jint JNICALL METHOD_NAME(IsoPacketDescriptor, length)
         unwrapIsoPacketDescriptor(env, this);
     if (!isopacket) return 0;
 
-    return isopacket->length;
+    return (jint) isopacket->length;
 }
 
 /**
@@ -55,7 +55,7 @@ JNIEXPORT void JNICALL METHOD_NAME(IsoPacketDescriptor, setLength)
         unwrapIsoPacketDescriptor(env, this);
     if (!isopacket) return;
 
-    isopacket->length = length;
+    isopacket->length = (unsigned int) length;
 }
 
 /**
@@ -70,7 +70,7 @@ JNIEXPORT jint JNICALL METHOD_NAME(IsoPacketDescriptor, actualLength)
         unwrapIsoPacketDescriptor(env, this);
     if (!isopacket) return 0;
 
-    return isopacket->actual_length;
+    return (jint) isopacket->actual_length;
 }
 
 /**
diff --git a/src/main/c/src/LibUsb.c b/src/main/c/src/LibUsb.c
index 97e556f..6da314a 100644
--- a/src/main/c/src/LibUsb.c
+++ b/src/main/c/src/LibUsb.c
@@ -120,8 +120,8 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, getDeviceList)
 
     libusb_device **list;
     ssize_t result = libusb_get_device_list(ctx, &list);
-    if (result >= 0) setDeviceList(env, list, result, deviceList);
-    return result;
+    if (result >= 0) setDeviceList(env, list, (jint) result, deviceList);
+    return (jint) result;
 }
 
 /**
@@ -193,7 +193,7 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, getPortPath)
     #if defined(LIBUSBX_API_VERSION)
         jlong path_size = (*env)->GetDirectBufferCapacity(env, path);
 
-        return libusb_get_port_path(ctx, dev, path_ptr, path_size);
+        return libusb_get_port_path(ctx, dev, path_ptr, (uint8_t) path_size);
     #else
         return 0;
     #endif
@@ -260,7 +260,7 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, getMaxPacketSize)
     libusb_device *dev = unwrapDevice(env, device);
     if (!dev) return 0;
 
-    return libusb_get_max_packet_size(dev, endpoint);
+    return libusb_get_max_packet_size(dev, (unsigned char) endpoint);
 }
 
 /**
@@ -275,7 +275,7 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, getMaxIsoPacketSize)
     libusb_device *dev = unwrapDevice(env, device);
     if (!dev) return 0;
 
-    return libusb_get_max_iso_packet_size(dev, endpoint);
+    return libusb_get_max_iso_packet_size(dev, (unsigned char) endpoint);
 }
 
 /**
@@ -342,7 +342,7 @@ JNIEXPORT jobject JNICALL METHOD_NAME(LibUsb, openDeviceWithVidPid)
     if (!ctx && context) return NULL;
 
     return wrapDeviceHandle(env, libusb_open_device_with_vid_pid(
-        ctx, vendorId, productId));
+        ctx, (uint16_t) vendorId, (uint16_t) productId));
 }
 
 /**
@@ -472,7 +472,7 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, clearHalt)
     libusb_device_handle *dev_handle = unwrapDeviceHandle(env, handle);
     if (!dev_handle) return 0;
 
-    return libusb_clear_halt(dev_handle, endpoint);
+    return libusb_clear_halt(dev_handle, (unsigned char) endpoint);
 }
 
 /**
@@ -543,7 +543,7 @@ JNIEXPORT jboolean JNICALL METHOD_NAME(LibUsb, hasCapability)
     JNIEnv *env, jclass class, jint capability
 )
 {
-    return libusb_has_capability(capability);
+    return (jboolean) libusb_has_capability((uint32_t) capability);
 }
 
 /**
@@ -565,7 +565,7 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, le16ToCpu)
     JNIEnv *env, jclass class, jint x
 )
 {
-    return libusb_le16_to_cpu(x);
+    return libusb_le16_to_cpu((uint16_t) x);
 }
 
 /**
@@ -576,7 +576,7 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, cpuToLe16)
     JNIEnv *env, jclass class, jint x
 )
 {
-    return libusb_cpu_to_le16(x);
+    return libusb_cpu_to_le16((uint16_t) x);
 }
 
 /**
@@ -642,7 +642,7 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, getStringDescriptorAscii)
     // and then +1 for the terminating NUL byte for C strings (the descriptor itself doesn't necessarily have one!).
     unsigned char buffer[127 + 1];
     int result = libusb_get_string_descriptor_ascii(
-        dev_handle, index, buffer, 127);
+        dev_handle, (uint8_t) index, buffer, 127);
     if (result >= 0)
     {
         buffer[result] = 0x00;
@@ -689,7 +689,7 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, getConfigDescriptor)
     if (!dev) return 0;
 
     struct libusb_config_descriptor *config;
-    int result = libusb_get_config_descriptor(dev, index, &config);
+    int result = libusb_get_config_descriptor(dev, (uint8_t) index, &config);
     if (result == LIBUSB_SUCCESS) setConfigDescriptor(env, config, descriptor);
     return result;
 }
@@ -710,7 +710,7 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, getConfigDescriptorByValue)
 
     struct libusb_config_descriptor *config;
     int result = libusb_get_config_descriptor_by_value(
-        dev, index, &config);
+        dev, (uint8_t) index, &config);
     if (result == LIBUSB_SUCCESS) setConfigDescriptor(env, config, descriptor);
     return result;
 }
@@ -748,8 +748,9 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, controlTransfer)
     if (!dev_handle) return 0;
 
     jlong data_size = (*env)->GetDirectBufferCapacity(env, data);
-    return libusb_control_transfer(dev_handle, bmRequestType, bRequest,
-        wValue, wIndex, data_ptr, data_size, timeout);
+    return libusb_control_transfer(dev_handle, (uint8_t) bmRequestType,
+        (uint8_t) bRequest, (uint16_t) wValue, (uint16_t) wIndex, data_ptr,
+        (uint16_t) data_size, (unsigned int) timeout);
 }
 
 /**
@@ -770,8 +771,8 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, bulkTransfer)
 
     int sent;
     jlong data_size = (*env)->GetDirectBufferCapacity(env, data);
-    int result = libusb_bulk_transfer(dev_handle, endpoint, data_ptr, data_size, &sent,
-        timeout);
+    int result = libusb_bulk_transfer(dev_handle, (unsigned char) endpoint,
+        data_ptr, (int) data_size, &sent, (unsigned int) timeout);
     if (result == LIBUSB_SUCCESS)
     {
         jclass cls = (*env)->GetObjectClass(env, transferred);
@@ -800,8 +801,8 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, interruptTransfer)
 
     int sent;
     jlong data_size = (*env)->GetDirectBufferCapacity(env, data);
-    int result = libusb_interrupt_transfer(dev_handle, endpoint, data_ptr, data_size,
-        &sent, timeout);
+    int result = libusb_interrupt_transfer(dev_handle, (unsigned char) endpoint,
+        data_ptr, (int) data_size, &sent, (unsigned int) timeout);
     if (result == LIBUSB_SUCCESS)
     {
         jclass cls = (*env)->GetObjectClass(env, transferred);
@@ -922,8 +923,8 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, waitForEvent)
     if (!ctx && context) return 0;
 
     struct timeval tv;
-    tv.tv_sec = timeout / 1000000;
-    tv.tv_usec = timeout % 1000000;
+    tv.tv_sec = (long int) timeout / 1000000;
+    tv.tv_usec = (long int) timeout % 1000000;
 
     return libusb_wait_for_event(ctx, &tv);
 }
@@ -938,7 +939,8 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, handleEventsTimeoutCompleted)
 )
 {
     int *complete = NULL;
-    if (completed) {
+    if (completed)
+    {
         DIRECT_BUFFER(env, completed, complete_tmp, return 0);
         complete = (int *) complete_tmp;
     }
@@ -947,8 +949,8 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, handleEventsTimeoutCompleted)
     if (!ctx && context) return 0;
 
     struct timeval tv;
-    tv.tv_sec = timeout / 1000000;
-    tv.tv_usec = timeout % 1000000;
+    tv.tv_sec = (long int) timeout / 1000000;
+    tv.tv_usec = (long int) timeout % 1000000;
 
     return libusb_handle_events_timeout_completed(ctx, &tv, complete);
 }
@@ -965,8 +967,8 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, handleEventsTimeout)
     if (!ctx && context) return 0;
 
     struct timeval tv;
-    tv.tv_sec = timeout / 1000000;
-    tv.tv_usec = timeout % 1000000;
+    tv.tv_sec = (long int) timeout / 1000000;
+    tv.tv_usec = (long int) timeout % 1000000;
 
     return libusb_handle_events_timeout(ctx, &tv);
 }
@@ -994,7 +996,8 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, handleEventsCompleted)
 )
 {
     int *complete = NULL;
-    if (completed) {
+    if (completed)
+    {
         DIRECT_BUFFER(env, completed, complete_tmp, return 0);
         complete = (int *) complete_tmp;
     }
@@ -1017,8 +1020,8 @@ JNIEXPORT jint JNICALL METHOD_NAME(LibUsb, handleEventsLocked)
     if (!ctx && context) return 0;
 
     struct timeval tv;
-    tv.tv_sec = timeout / 1000000;
-    tv.tv_usec = timeout % 1000000;
+    tv.tv_sec = (long int) timeout / 1000000;
+    tv.tv_usec = (long int) timeout % 1000000;
 
     return libusb_handle_events_locked(ctx, &tv);
 }
@@ -1145,7 +1148,7 @@ JNIEXPORT jobject JNICALL METHOD_NAME(LibUsb, allocTransfer)
     }
 
     transfer->user_data = transferData;
-    transferData->maxNumIsoPackets = isoPackets;
+    transferData->maxNumIsoPackets = (size_t) isoPackets;
 
     jobject transferObject = wrapTransfer(env, transfer);
 
diff --git a/src/main/c/src/Makefile.am b/src/main/c/src/Makefile.am
index 95ebe12..5b7cda4 100644
--- a/src/main/c/src/Makefile.am
+++ b/src/main/c/src/Makefile.am
@@ -1,10 +1,9 @@
 lib_LTLIBRARIES = libusb4java.la
-libusb4java_la_CFLAGS = -Wall -Werror $(LIBUSB_CFLAGS)
+libusb4java_la_CFLAGS = -pedantic -Wall -Wextra -Wformat=2 -Winit-self -Wunused -Wno-unused-parameter -Wuninitialized -Wundef -Wshadow -Wbad-function-cast -Wcast-qual -Wcast-align -Wwrite-strings -Wconversion -Wlogical-op -Wstrict-prototypes -Wredundant-decls -Wnested-externs $(LIBUSB_CFLAGS)
 libusb4java_la_LIBADD = $(LIBUSB_LIBS)
 libusb4java_la_LDFLAGS = -version-info 1:0:0 -no-undefined
 EXTRA_DIST = *.h
 libusb4java_la_SOURCES = \
-    wrappers.c \
     usb4java.c \
     LibUsb.c \
     Version.c \
diff --git a/src/main/c/src/Transfer.c b/src/main/c/src/Transfer.c
index 6059524..79da173 100644
--- a/src/main/c/src/Transfer.c
+++ b/src/main/c/src/Transfer.c
@@ -40,9 +40,8 @@ JNIEXPORT void JNICALL METHOD_NAME(Transfer, setDevHandle)
     JNIEnv *env, jobject this, jobject handle
 )
 {
-    NOT_NULL(env, handle, return);
     libusb_device_handle *dev_handle = unwrapDeviceHandle(env, handle);
-    if (!dev_handle) return;
+    if (!dev_handle && handle) return;
     struct libusb_transfer *transfer = unwrapTransfer(env, this);
     if (!transfer) return;
 
@@ -74,7 +73,7 @@ JNIEXPORT void JNICALL METHOD_NAME(Transfer, setFlags)
     struct libusb_transfer *transfer = unwrapTransfer(env, this);
     if (!transfer) return;
 
-    transfer->flags = flags;
+    transfer->flags = (uint8_t) flags;
 }
 
 /**
@@ -88,7 +87,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(Transfer, flags)
     struct libusb_transfer *transfer = unwrapTransfer(env, this);
     if (!transfer) return 0;
 
-    return transfer->flags;
+    return (jbyte) transfer->flags;
 }
 
 /**
@@ -102,7 +101,7 @@ JNIEXPORT void JNICALL METHOD_NAME(Transfer, setEndpoint)
     struct libusb_transfer *transfer = unwrapTransfer(env, this);
     if (!transfer) return;
 
-    transfer->endpoint = endpoint;
+    transfer->endpoint = (unsigned char) endpoint;
 }
 
 /**
@@ -116,7 +115,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(Transfer, endpoint)
     struct libusb_transfer *transfer = unwrapTransfer(env, this);
     if (!transfer) return 0;
 
-    return transfer->endpoint;
+    return (jbyte) transfer->endpoint;
 }
 
 /**
@@ -130,7 +129,7 @@ JNIEXPORT void JNICALL METHOD_NAME(Transfer, setType)
     struct libusb_transfer *transfer = unwrapTransfer(env, this);
     if (!transfer) return;
 
-    transfer->type = type;
+    transfer->type = (unsigned char) type;
 }
 
 /**
@@ -144,7 +143,7 @@ JNIEXPORT jbyte JNICALL METHOD_NAME(Transfer, type)
     struct libusb_transfer *transfer = unwrapTransfer(env, this);
     if (!transfer) return 0;
 
-    return transfer->type;
+    return (jbyte) transfer->type;
 }
 
 /**
@@ -158,7 +157,7 @@ JNIEXPORT void JNICALL METHOD_NAME(Transfer, setTimeout)
     struct libusb_transfer *transfer = unwrapTransfer(env, this);
     if (!transfer) return;
 
-    transfer->timeout = timeout;
+    transfer->timeout = (unsigned int) timeout;
 }
 
 /**
@@ -172,7 +171,7 @@ JNIEXPORT jint JNICALL METHOD_NAME(Transfer, timeout)
     struct libusb_transfer *transfer = unwrapTransfer(env, this);
     if (!transfer) return 0;
 
-    return transfer->timeout;
+    return (jint) transfer->timeout;
 }
 
 /**
@@ -430,8 +429,13 @@ JNIEXPORT void JNICALL METHOD_NAME(Transfer, setBufferNative)
     JNIEnv *env, jobject this, jobject buffer
 )
 {
-    NOT_NULL(env, buffer, return);
-    DIRECT_BUFFER(env, buffer, buffer_ptr, return);
+    unsigned char *buffer_ptr = NULL;
+    if (buffer)
+    {
+        DIRECT_BUFFER(env, buffer, buffer_tmp, return);
+        buffer_ptr = buffer_tmp;
+    }
+
     struct libusb_transfer *transfer = unwrapTransfer(env, this);
     if (!transfer) return;
 
@@ -452,7 +456,7 @@ JNIEXPORT void JNICALL METHOD_NAME(Transfer, setNumIsoPackets)
     // Check that calls to setNumIsoPackets() never set a number exceeding
     // the maximum, which was originally set at allocTransfer() time.
     if (((struct transfer_data *) transfer->user_data)->maxNumIsoPackets
-        < numIsoPackets)
+        < (size_t) numIsoPackets)
     {
         illegalArgument(env,
             "numIsoPackets exceeds maximum allowed number set with allocTransfer()");
diff --git a/src/main/c/src/usb4java.c b/src/main/c/src/usb4java.c
index 9fc6b10..ebcd1cc 100644
--- a/src/main/c/src/usb4java.c
+++ b/src/main/c/src/usb4java.c
@@ -7,13 +7,13 @@
 
 JavaVM *jvm = NULL;
 
-jint illegalArgument(JNIEnv *env, char *message)
+jint illegalArgument(JNIEnv *env, const char *message)
 {
     jclass cls = (*env)->FindClass(env, "java/lang/IllegalArgumentException");
     return (*env)->ThrowNew(env, cls, message);
 }
 
-jint illegalState(JNIEnv *env, char *message)
+jint illegalState(JNIEnv *env, const char *message)
 {
     jclass cls = (*env)->FindClass(env, "java/lang/IllegalStateException");
     return (*env)->ThrowNew(env, cls, message);
diff --git a/src/main/c/src/usb4java.h b/src/main/c/src/usb4java.h
index 24fcf91..0ca325f 100644
--- a/src/main/c/src/usb4java.h
+++ b/src/main/c/src/usb4java.h
@@ -86,7 +86,7 @@
 
 extern JavaVM *jvm;
 
-jint illegalArgument(JNIEnv *env, char *message);
-jint illegalState(JNIEnv *env, char *message);
+jint illegalArgument(JNIEnv *env, const char *message);
+jint illegalState(JNIEnv *env, const char *message);
 
 #endif
diff --git a/src/main/c/src/wrappers.c b/src/main/c/src/wrappers.c
deleted file mode 100644
index da85ad0..0000000
--- a/src/main/c/src/wrappers.c
+++ /dev/null
@@ -1,15 +0,0 @@
-/*
- * Copyright (C) 2013 Klaus Reimer (k@ailis.de)
- * See COPYING file for copying conditions
- */
-
-#include <string.h>
-
-// Enforce usage of older memcpy to be compatible with older libc versions
-#if WRAP_MEMCPY
-asm (".symver memcpy, memcpy@GLIBC_2.2.5");
-void *__wrap_memcpy(void *dest, const void *src, size_t n)
-{
-    return memcpy(dest, src, n);
-}
-#endif
diff --git a/src/main/java/de/ailis/usb4java/libusb/Transfer.java b/src/main/java/de/ailis/usb4java/libusb/Transfer.java
index 72754ae..739e65d 100644
--- a/src/main/java/de/ailis/usb4java/libusb/Transfer.java
+++ b/src/main/java/de/ailis/usb4java/libusb/Transfer.java
@@ -248,8 +248,15 @@ public final class Transfer
         // Native call.
         setBufferNative(buffer);
 
-        // Set new length. The native call above ensures that buffer isn't null.
-        setLengthNative(buffer.capacity());
+        if (buffer != null)
+        {
+            // Set new length based on buffer's capacity.
+            setLengthNative(buffer.capacity());
+        }
+        else
+        {
+            setLengthNative(0);
+        }
 
         // Once we know the native calls have gone through, update the
         // reference.