diff --git a/src/build.py b/src/build.py
index 67f3f5e..4dd6ee4 100755
--- a/src/build.py
+++ b/src/build.py
@@ -1615,6 +1615,8 @@ def ExecuteEmscriptenTestSuite(name, tests, config, outdir, warn_only=False):
   buildbot.Step('Execute emscripten testsuite (%s)' % name)
   Mkdir(outdir)
   try:
+    proc.check_call([os.path.join(NodeBinDir(), 'npm'), 'install'],
+                    cwd=GetInstallDir('emscripten'))
     proc.check_call(
         [GetInstallDir('emscripten', 'tests', 'runner.py'),
          '--em-config', config] + tests,