diff --git a/CHANGELOG.md b/CHANGELOG.md
index ad7b664cb..c457ebacf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -77,6 +77,7 @@ This project uses the changelog in accordance with [keepchangelog](http://keepac
 - Fixed `hf 14a sim` - a dynamic response now gets a modulation buffer sized to fit it, instead of one 68 bytes too small (or 1788 too large for ST25TA) (@iceman1001)
 - Fixed `BigBuf_malloc` - takes a uint32_t, so a request of 64KB or more fails instead of wrapping to zero (@iceman1001)
 - Fixed `BigBuf_max_traceLen` - returns a uint32_t, so LF sampling on a device with more than 64KB of BigBuf is not handed a truncated buffer (@iceman1001)
+- Fixed PM5 BigBuf allocation
 - Changed `hf mf view` - now show which VIGIK fields are RSA signed (@iceman1001)
 - Changed `hw status` - now reports EMULATOR memory (@iceman1001)
 - Changed `hf mf view` - Urmet Captiv cards now decode their number field and data regions (@iceman1001)
diff --git a/armsrc/BigBuf.c b/armsrc/BigBuf.c
index 6ec041ec8..a3172ffb5 100644
--- a/armsrc/BigBuf.c
+++ b/armsrc/BigBuf.c
@@ -23,7 +23,7 @@
 #include "util.h" // nbytes
 
 #define BIGBUF_ALIGN_BYTES (4)
-#define BIGBUF_ALIGN_MASK  (0xFFFF + 1 - BIGBUF_ALIGN_BYTES)
+#define BIGBUF_ALIGN_MASK  (~(uint32_t)(BIGBUF_ALIGN_BYTES - 1))
 
 extern uint32_t _stack_start[], __bss_end__[];