diff --git a/grade-diffs.py b/grade-diffs.py
index a723a9c..2422f5a 100755
--- a/grade-diffs.py
+++ b/grade-diffs.py
@@ -104,7 +104,7 @@ def lineToTestAnnotation(args,line,linenumber):
 def loadResultsJsonIfExists(inputfile):
   default_results = { "tests" : [] }
 
-  if inputfile = "":
+  if inputfile == "":
     return default_results
 
   try: