diff --git "a/claudetool/onstart/testdata/Makefile-\346\227\245\346\234\254\350\252\236" "b/claudetool/onstart/testdata/Makefile-\346\227\245\346\234\254\350\252\236"
new file mode 100644
index 0000000..c78f45a
--- /dev/null
+++ "b/claudetool/onstart/testdata/Makefile-\346\227\245\346\234\254\350\252\236"
@@ -0,0 +1,10 @@
+# Makefile with Japanese characters in filename
+# This should be categorized as a build file
+
+all:
+	echo "Building with Japanese characters in Makefile name"
+
+clean:
+	rm -f *.o
+
+.PHONY: all clean