diff --git a/Lib/test/test_import.py b/Lib/test/test_import.py
index 9f80b70..e4d5332 100644
--- a/Lib/test/test_import.py
+++ b/Lib/test/test_import.py
@@ -380,7 +380,7 @@
     def test_foreign_code(self):
         py_compile.compile(self.file_name)
         with open(self.compiled_name, "rb") as f:
-            header = f.read(8)
+            header = f.read(12)
             code = marshal.load(f)
         constants = list(code.co_consts)
         foreign_code = test_main.__code__
@@ -644,6 +644,16 @@
         self.assertEqual(sys.modules['pep3147.foo'].__cached__,
                          os.path.join(os.curdir, foo_pyc))
 
+    def test_recompute_pyc_same_second(self):
+        # Even when the source file doesn't change timestamp, a change in
+        # source size is enough to trigger recomputation of the pyc file.
+        __import__(TESTFN)
+        unload(TESTFN)
+        with open(self.source, 'a') as fp:
+            print("x = 5", file=fp)
+        m = __import__(TESTFN)
+        self.assertEqual(m.x, 5)
+
 
 class RelativeImportFromImportlibTests(test_relative_imports.RelativeImports):
 
diff --git a/Lib/test/test_zipimport.py b/Lib/test/test_zipimport.py
index 56141ef..358910b 100644
--- a/Lib/test/test_zipimport.py
+++ b/Lib/test/test_zipimport.py
@@ -19,7 +19,7 @@
 from traceback import extract_tb, extract_stack, print_tb
 raise_src = 'def do_raise(): raise TypeError\n'
 
-def make_pyc(co, mtime):
+def make_pyc(co, mtime, size):
     data = marshal.dumps(co)
     if type(mtime) is type(0.0):
         # Mac mtimes need a bit of special casing
@@ -27,14 +27,14 @@
             mtime = int(mtime)
         else:
             mtime = int(-0x100000000 + int(mtime))
-    pyc = imp.get_magic() + struct.pack("<i", int(mtime)) + data
+    pyc = imp.get_magic() + struct.pack("<ii", int(mtime), size & 0xFFFFFFFF) + data
     return pyc
 
 def module_path_to_dotted_name(path):
     return path.replace(os.sep, '.')
 
 NOW = time.time()
-test_pyc = make_pyc(test_co, NOW)
+test_pyc = make_pyc(test_co, NOW, len(test_src))
 
 
 TESTMOD = "ziptestmodule"
@@ -293,7 +293,7 @@
             return __file__
         if __loader__.get_data("some.data") != b"some data":
             raise AssertionError("bad data")\n"""
-        pyc = make_pyc(compile(src, "<???>", "exec"), NOW)
+        pyc = make_pyc(compile(src, "<???>", "exec"), NOW, len(src))
         files = {TESTMOD + pyc_ext: (NOW, pyc),
                  "some.data": (NOW, "some data")}
         self.doTest(pyc_ext, files, TESTMOD)
@@ -313,7 +313,7 @@
         self.doTest(".py", files, TESTMOD, call=self.assertModuleSource)
 
     def testGetCompiledSource(self):
-        pyc = make_pyc(compile(test_src, "<???>", "exec"), NOW)
+        pyc = make_pyc(compile(test_src, "<???>", "exec"), NOW, len(test_src))
         files = {TESTMOD + ".py": (NOW, test_src),
                  TESTMOD + pyc_ext: (NOW, pyc)}
         self.doTest(pyc_ext, files, TESTMOD, call=self.assertModuleSource)