diff --git a/py/persistentcode.c b/py/persistentcode.c
index 07395b304b..5cb5117093 100644
--- a/py/persistentcode.c
+++ b/py/persistentcode.c
@@ -38,6 +38,9 @@
 
 #include "py/smallint.h"
 
+// The current version of .mpy files
+#define MPY_VERSION (1)
+
 // The feature flags byte encodes the compile-time config options that
 // affect the generate bytecode.
 #define MPY_FEATURE_FLAGS ( \
@@ -209,10 +212,10 @@ STATIC mp_raw_code_t *load_raw_code(mp_reader_t *reader) {
 mp_raw_code_t *mp_raw_code_load(mp_reader_t *reader) {
     byte header[4];
     read_bytes(reader, header, sizeof(header));
-    if (strncmp((char*)header, "M\x00", 2) != 0) {
-        mp_raise_ValueError("invalid .mpy file");
-    }
-    if (header[2] != MPY_FEATURE_FLAGS || header[3] > mp_small_int_bits()) {
+    if (header[0] != 'M'
+        || header[1] != MPY_VERSION
+        || header[2] != MPY_FEATURE_FLAGS
+        || header[3] > mp_small_int_bits()) {
         mp_raise_ValueError("incompatible .mpy file");
     }
     mp_raw_code_t *rc = load_raw_code(reader);
@@ -359,7 +362,7 @@ void mp_raw_code_save(mp_raw_code_t *rc, mp_print_t *print) {
     //  byte  version
     //  byte  feature flags
     //  byte  number of bits in a small int
-    byte header[4] = {'M', 0, MPY_FEATURE_FLAGS_DYNAMIC,
+    byte header[4] = {'M', MPY_VERSION, MPY_FEATURE_FLAGS_DYNAMIC,
         #if MICROPY_DYNAMIC_COMPILER
         mp_dynamic_compiler.small_int_bits,
         #else
diff --git a/tools/mpy-tool.py b/tools/mpy-tool.py
index ce373a4f5b..d14e0f4ea4 100755
--- a/tools/mpy-tool.py
+++ b/tools/mpy-tool.py
@@ -57,6 +57,7 @@ class FreezeError(Exception):
         return 'error while freezing %s: %s' % (self.rawcode.source_file, self.msg)
 
 class Config:
+    MPY_VERSION = 1
     MICROPY_LONGINT_IMPL_NONE = 0
     MICROPY_LONGINT_IMPL_LONGLONG = 1
     MICROPY_LONGINT_IMPL_MPZ = 2
@@ -438,8 +439,8 @@ def read_mpy(filename):
         header = bytes_cons(f.read(4))
         if header[0] != ord('M'):
             raise Exception('not a valid .mpy file')
-        if header[1] != 0:
-            raise Exception('incompatible version')
+        if header[1] != config.MPY_VERSION:
+            raise Exception('incompatible .mpy version')
         feature_flags = header[2]
         config.MICROPY_OPT_CACHE_MAP_LOOKUP_IN_BYTECODE = (feature_flags & 1) != 0
         config.MICROPY_PY_BUILTINS_STR_UNICODE = (feature_flags & 2) != 0