diff --git a/blkmaker.c b/blkmaker.c
index 58752a4..6c5918f 100644
--- a/blkmaker.c
+++ b/blkmaker.c
@@ -56,7 +56,7 @@ bool build_merkle_root(unsigned char *mrklroot_out, blktemplate_t *tmpl, unsigne
 static const int cbScriptSigLen = 4 + 1 + 36;
 
 static
-bool _blkmk_append_cb(blktemplate_t *tmpl, void *vout, void *append, size_t appendsz) {
+bool _blkmk_append_cb(blktemplate_t *tmpl, void *vout, const void *append, size_t appendsz) {
 	unsigned char *out = vout;
 	unsigned char *in = tmpl->cbtxn->data;
 	size_t insz = tmpl->cbtxn->datasz;
@@ -83,7 +83,7 @@ bool _blkmk_append_cb(blktemplate_t *tmpl, void *vout, void *append, size_t appe
 	return true;
 }
 
-ssize_t blkmk_append_coinbase_safe(blktemplate_t *tmpl, void *append, size_t appendsz) {
+ssize_t blkmk_append_coinbase_safe(blktemplate_t *tmpl, const void *append, size_t appendsz) {
 	if (!(tmpl->mutations & (BMM_CBAPPEND | BMM_CBSET)))
 		return -1;
 	
diff --git a/blkmaker.h b/blkmaker.h
index 717a592..10680d4 100644
--- a/blkmaker.h
+++ b/blkmaker.h
@@ -10,7 +10,7 @@
 
 extern bool (*blkmk_sha256_impl)(void *hash_out, const void *data, size_t datasz);
 
-extern ssize_t blkmk_append_coinbase_safe(blktemplate_t *, void *append, size_t appendsz);
+extern ssize_t blkmk_append_coinbase_safe(blktemplate_t *, const void *append, size_t appendsz);
 extern bool _blkmk_extranonce(blktemplate_t *tmpl, void *vout, unsigned int workid, size_t *offs);
 extern size_t blkmk_get_data(blktemplate_t *, void *buf, size_t bufsz, time_t usetime, int16_t *out_expire, unsigned int *out_dataid);
 extern blktime_diff_t blkmk_time_left(const blktemplate_t *, time_t nowtime);