diff --git a/hack/util.py b/hack/util.py
index 1dc63dd2a..8733cca38 100644
--- a/hack/util.py
+++ b/hack/util.py
@@ -7,11 +7,15 @@
 import yaml
 
 
-def walk_yaml(directory, revision=None):
+def walk_yaml(directory, revision=None, allowed_extensions=None):
     if revision is None:
         for root, _, files in os.walk(directory):
             for filename in files:
                 if not filename.endswith('.yaml'):
+                    if allowed_extensions:
+                        _, ext = os.path.splitext(filename)
+                        if ext not in allowed_extensions:
+                            raise ValueError('invalid filename: {!r} (allowed extensions: {})'.format(os.path.join(root, filename), allowed_extensions))
                     continue
                 path = os.path.join(root, filename)
                 with open(path) as f:
diff --git a/hack/validate-blocked-edges.py b/hack/validate-blocked-edges.py
index ce864480d..ac0b0b526 100755
--- a/hack/validate-blocked-edges.py
+++ b/hack/validate-blocked-edges.py
@@ -6,7 +6,7 @@
 
 
 def validate_blocked_edges(directory):
-    for path, data in util.walk_yaml(directory=directory):
+    for path, data in util.walk_yaml(directory=directory, allowed_extensions=('.yaml',)):
         try:
             validate_blocked_edge(data=data)
         except Exception as error: