diff --git a/testing/mochitest/runtests.py b/testing/mochitest/runtests.py
index d7201c696468..634be99b6be8 100644
--- a/testing/mochitest/runtests.py
+++ b/testing/mochitest/runtests.py
@@ -1755,6 +1755,7 @@ class Mochitest(MochitestUtilsMixin):
     options.totalChunks = None
     options.thisChunk = None
     options.chunkByDir = 0
+    result = 1 # default value, if no tests are run.
     inputTestPath = self.getTestPath(options)
     for dir in dirs:
       if inputTestPath and not inputTestPath.startswith(dir):