diff --git a/capnpy/compiler/module.py b/capnpy/compiler/module.py
index bf5d4c7e..abc3dec4 100644
--- a/capnpy/compiler/module.py
+++ b/capnpy/compiler/module.py
@@ -130,7 +130,7 @@ def register_import(self, fname):
         name = '_%s_capnp' % name
         if name in self.importnames.values():
             # avoid name clashes
-            name = '%s_%s' % (name, len(self.filenames))
+            name = '%s_%s' % (name, len(self.importnames))
         self.importnames[fname] = name
         return name