diff --git a/styleguide/format.py b/styleguide/format.py
index 27e0f0b1bf..1b65cb5a47 100755
--- a/styleguide/format.py
+++ b/styleguide/format.py
@@ -42,6 +42,10 @@ clangExec = "clang-format"
 if sys.platform.startswith("win32"):
     clangExec += ".exe"
 
+if not files:
+    print("Error: no files found to format", file=sys.stderr)
+    sys.exit(1)
+
 for name in files:
     # List names of files as they are processed if verbose flag was given
     if len(sys.argv) > 1 and sys.argv[1] == "-v":