diff --git a/cli/signit.py b/cli/signit.py
index fd33dca9..f6a37fb7 100755
--- a/cli/signit.py
+++ b/cli/signit.py
@@ -293,8 +293,12 @@ def doit(keydir, outfn=None, build_dir=None, high_water=False,
         # bugfix: size must be non-page aligned, so extra bytes are erased past end
         if (body_len % 4096) == 0:
             body_len += 512
-
-    assert body_len % 512 == 0, body_len
+        assert body_len % 512 == 0, body_len
+    else:
+        # bugfix: PSRAM-based products (Mk4, Q1) need to erase 4k blocks, so
+        # trouble happens if final binary isn't aligned to that size.
+        body_len = align_to(body_len, 4096)
+        assert body_len % 4096 == 0, body_len
 
     # pad out 
     vectors = pad_to(vectors, FW_HEADER_OFFSET)
diff --git a/releases/ChangeLog.md b/releases/ChangeLog.md
index 3ac4c60a..97bc4a45 100644
--- a/releases/ChangeLog.md
+++ b/releases/ChangeLog.md
@@ -1,3 +1,7 @@
+## 5.1.4 - 2023-09-08
+
+- Bugfix: Most users would see a red light after upgrade to 5.1.3 from 5.1.2. Fixed.
+
 ## 5.1.3 - 2023-09-07
 
 - New Feature: Batch sign multiple PSBT files. `Advanced/Tools -> File Management -> Batch Sign PSBT`
diff --git a/stm32/mk4-bootloader/psram.c b/stm32/mk4-bootloader/psram.c
index 1037da54..f8119bac 100644
--- a/stm32/mk4-bootloader/psram.c
+++ b/stm32/mk4-bootloader/psram.c
@@ -335,7 +335,7 @@ psram_do_upgrade(const uint8_t *start, uint32_t size)
         if(dest % FLASH_ERASE_SIZE == 0) {
             // page erase as we go
             rv = flash_page_erase(dest);
-#if 1
+#if 0
             if(rv) {
                 puts2("erase rv=");
                 puthex2(rv);
@@ -347,7 +347,7 @@ psram_do_upgrade(const uint8_t *start, uint32_t size)
 
         memcpy(&tmp, start+pos, 8);
         rv = flash_burn(dest, tmp);
-#if 1
+#if 0
         if(rv) {
             puts2("burn rv=");
             puthex2(rv);
diff --git a/stm32/mk4-bootloader/verify.c b/stm32/mk4-bootloader/verify.c
index 7bc40651..4843e776 100644
--- a/stm32/mk4-bootloader/verify.c
+++ b/stm32/mk4-bootloader/verify.c
@@ -102,7 +102,8 @@ checksum_flash(uint8_t fw_digest[32], uint8_t world_digest[32], uint32_t fw_leng
     const uint8_t *base = (const uint8_t *)BL_FLASH_BASE;
     checksum_more(&ctx, &total_len, base, ((uint8_t *)MCU_KEYS)-base);
 
-    // Probably-blank area after firmware, and filesystem area
+    // Probably-blank area after firmware, and filesystem area.
+    // Important: firmware images (fw_length) must be aligned with flash erase unit size (4k).
     const uint8_t *fs = start + fw_length;
     const uint8_t *last = base + MAIN_FLASH_SIZE;
     checksum_more(&ctx, &total_len, fs, last-fs);