diff --git a/comtypes/client/_generate.py b/comtypes/client/_generate.py
index f4f5fcfd..f6827bec 100644
--- a/comtypes/client/_generate.py
+++ b/comtypes/client/_generate.py
@@ -3,6 +3,7 @@
 import sys
 import comtypes.client
 import comtypes.tools.codegenerator
+import imp
 
 import logging
 logger = logging.getLogger(__name__)
@@ -23,7 +24,11 @@ def _my_import(fullname):
     if comtypes.client.gen_dir \
            and comtypes.client.gen_dir not in comtypes.gen.__path__:
         comtypes.gen.__path__.append(comtypes.client.gen_dir)
-    return __import__(fullname, globals(), locals(), ['DUMMY'])
+
+    mod = imp.reload(eval(fullname)) if fullname in sys.modules \
+            else __import__(fullname, globals(), locals(), ['DUMMY'])
+    mod._comtypes_validate_file()
+    return mod
 
 def _name_module(tlib):
     # Determine the name of a typelib wrapper module.
@@ -152,8 +157,10 @@ def _CreateWrapper(tlib, pathname=None):
     # helper which creates and imports the real typelib wrapper module.
     fullname = _name_module(tlib)
     try:
-        return sys.modules[fullname]
-    except KeyError:
+        mod = sys.modules[fullname]
+        mod._comtypes_validate_file()
+        return mod
+    except (KeyError, AttributeError):
         pass
 
     modname = fullname.split(".")[-1]
@@ -165,11 +172,9 @@ def _CreateWrapper(tlib, pathname=None):
 
     # generate the module since it doesn't exist or is out of date
     from comtypes.tools.tlbparser import generate_module
-    if comtypes.client.gen_dir is None:
-        import cStringIO
-        ofi = cStringIO.StringIO()
-    else:
-        ofi = open(os.path.join(comtypes.client.gen_dir, modname + ".py"), "w")
+    import cStringIO
+    ofi = cStringIO.StringIO()
+
     # XXX use logging!
     if __verbose__:
         print "# Generating comtypes.gen.%s" % modname
@@ -184,7 +189,8 @@ def _CreateWrapper(tlib, pathname=None):
         sys.modules[fullname] = mod
         setattr(comtypes.gen, modname, mod)
     else:
-        ofi.close()
+        with open(os.path.join(comtypes.client.gen_dir, modname + ".py"), "w") as fd:
+            fd.write(ofi.getvalue())
         mod = _my_import(fullname)
     return mod
 
diff --git a/comtypes/tools/codegenerator.py b/comtypes/tools/codegenerator.py
index be0f0566..97436c78 100644
--- a/comtypes/tools/codegenerator.py
+++ b/comtypes/tools/codegenerator.py
@@ -258,6 +258,7 @@ def generate_code(self, items, filename=None):
         for line in wrapper.wrap(text):
             print >> self.output, line
         print >> self.output, "from comtypes import _check_version; _check_version(%r)" % version
+        print >> self.output, "def _comtypes_validate_file(): pass"
         return loops
 
     def type_name(self, t, generate=True):
@@ -627,7 +628,7 @@ def External(self, ext):
         modname = comtypes.client._generate._name_module(ext.tlib)
         ext.name = "%s.%s" % (modname, ext.symbol_name)
         self._externals[libdesc] = modname
-        print >> self.imports, "import", modname
+        print >> self.imports, "import %s; %s._comtypes_validate_file()" % (modname, modname)
         comtypes.client.GetModule(ext.tlib)
 
     def Constant(self, tp):