diff --git a/utils/tdiff.py b/utils/tdiff.py
--- a/utils/tdiff.py
+++ b/utils/tdiff.py
@@ -81,7 +81,7 @@
 def query_ninja(targets, cwd):
     # Query ninja for a node in its build dependency tree.
     proc = subprocess.Popen(
-        ["ninja", "-t", "query"] + targets,
+        ["ninja", "-t", "query"] + list(set(targets)),
         cwd=cwd,
         stdout=subprocess.PIPE,
         universal_newlines=True,