diff --git a/pytools/__init__.py b/pytools/__init__.py
index 7bc99bb919c8020ac6eeec0ae059c3184cfbf5eb..a9c58ce26e893daed48c17d6ca894080ceb82ac8 100644
--- a/pytools/__init__.py
+++ b/pytools/__init__.py
@@ -1855,10 +1855,9 @@ def generate_unique_names(prefix):
 
 
 def generate_numbered_unique_names(prefix, num=None):
-    orig_num = num
-    num = 0
-    if orig_num is None:
-        yield (num, prefix)
+    if num is None:
+        yield (0, prefix)
+        num = 0
 
     while True:
         name = "%s_%d" % (prefix, num)
diff --git a/test/test_pytools.py b/test/test_pytools.py
index d73553d97c639516a937f56786ffd3840a2519b2..5346c25591d142a5af4c3d677ec8b92d5f03bbe5 100644
--- a/test/test_pytools.py
+++ b/test/test_pytools.py
@@ -195,6 +195,17 @@ def test_diskdict():
         del d
 
 
+def test_generate_numbered_unique_names():
+    from pytools import generate_numbered_unique_names
+
+    gen = generate_numbered_unique_names("a")
+    assert next(gen) == (0, "a")
+    assert next(gen) == (1, "a_0")
+
+    gen = generate_numbered_unique_names("b", 6)
+    assert next(gen) == (7, "b_6")
+
+
 if __name__ == "__main__":
     if len(sys.argv) > 1:
         exec(sys.argv[1])