diff --git a/src/io.c b/src/io.c
index ad78c50f3..58014f8ed 100644
--- a/src/io.c
+++ b/src/io.c
@@ -17,8 +17,15 @@
 #include "io.h"
 
 static uint8_t *data_memory_base;
-/* set memory size to 2^32 bytes */
-#define MEM_SIZE 0x100000000ULL
+/* set memory size to 2^32 - 1 bytes
+ *
+ * In order to make rv32emu portable for both 32-bit and 64-bit systems, 
+ * we need keep the memory size to a maximum of 2^32 - 1 bytes, 
+ * this allows rv32emu to access every segment of memory in either environment. 
+ * Furthermore, it is safe since most test cases' data memory usage 
+ * will not exceed 0xFFFFFFFF for now.
+ */
+#define MEM_SIZE 0xFFFFFFFFULL
 
 memory_t *memory_new()
 {