diff --git a/Makefile b/Makefile
index 1e4915a6d2ebed..b18facf08eba85 100644
--- a/Makefile
+++ b/Makefile
@@ -294,6 +294,10 @@ jstest: build-addons build-js-native-api-tests build-node-api-tests ## Runs addo
 		$(CI_JS_SUITES) \
 		$(CI_NATIVE_SUITES)
 
+.PHONY: tooltest
+tooltest:
+	@$(PYTHON) test/tools/test-js2c.py
+
 .PHONY: coverage-run-js
 coverage-run-js:
 	$(RM) -r out/$(BUILDTYPE)/.coverage
@@ -311,6 +315,7 @@ test: all ## Runs default tests, linters, and builds docs.
 	$(MAKE) -s build-node-api-tests
 	$(MAKE) -s cctest
 	$(MAKE) -s jstest
+	$(MAKE) -s tooltest
 
 .PHONY: test-only
 test-only: all  ## For a quick test, does not run linter or build docs.
@@ -319,6 +324,7 @@ test-only: all  ## For a quick test, does not run linter or build docs.
 	$(MAKE) build-node-api-tests
 	$(MAKE) cctest
 	$(MAKE) jstest
+	$(MAKE) tooltest
 
 # Used by `make coverage-test`
 test-cov: all
diff --git a/test/tools/test-js2c.py b/test/tools/test-js2c.py
new file mode 100644
index 00000000000000..204562117086e4
--- /dev/null
+++ b/test/tools/test-js2c.py
@@ -0,0 +1,14 @@
+import unittest
+import sys, os
+sys.path.append(os.path.abspath(os.path.join(os.path.dirname(__file__),
+                                             '..', '..', 'tools')))
+from js2c import NormalizeFileName
+
+class Js2ctest(unittest.TestCase):
+    def testNormalizeFileName(self):
+        self.assertEqual(NormalizeFileName('dir/mod.js'), 'mod')
+        self.assertEqual(NormalizeFileName('deps/mod.js'), 'internal/deps/mod')
+        self.assertEqual(NormalizeFileName('mod.js'), 'mod')
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/tools/js2c.py b/tools/js2c.py
index 0189dd76291916..1346b2a87046d3 100755
--- a/tools/js2c.py
+++ b/tools/js2c.py
@@ -261,7 +261,8 @@ def NormalizeFileName(filename):
     split = ['internal'] + split
   else:  # `lib/**/*.js` so drop the 'lib' part
     split = split[1:]
-  filename = '/'.join(split)
+  if len(split):
+    filename = '/'.join(split)
   return os.path.splitext(filename)[0]