diff --git a/Makefile b/Makefile
index 38fe1f5c1d1443671abbd54cbba5669e94d49436..c2642ce0f71d552ff9b070ffead1e7264b8882e1 100644
--- a/Makefile
+++ b/Makefile
@@ -700,7 +700,7 @@ clean:
 
 tags:
 	ctags * -R
-	cscope -b `find . -name '*.cc'` `find . -name '*.h'`
+	cscope -b `find . -name '*.cc'` `find . -name '*.h'` `find . -name '*.c'`
 
 format:
 	build_tools/format-diff.sh