diff --git a/src/z_zone.c b/src/z_zone.c
index dae7dff0..10755608 100644
--- a/src/z_zone.c
+++ b/src/z_zone.c
@@ -242,7 +242,7 @@ void *Z_Malloc2(size_t size, INT32 tag, void *user, INT32 alignbits,
 void *Z_MallocAlign(size_t size, INT32 tag, void *user, INT32 alignbits)
 #endif
 {
-	size_t extrabytes = (1<<alignbits) - 1;
+	size_t extrabytes = (1<<alignbits) - (sizeof(size_t)*8 > (UINT32) alignbits); // only subtract 1 if the bit shift did not cause an overflow
 	size_t padsize = 0;
 	memblock_t *block;
 	void *ptr;