Index: Parser/asdl.py
===================================================================
--- Parser/asdl.py	(revision 62588)
+++ Parser/asdl.py	(working copy)
@@ -387,6 +387,10 @@
             self.visit(f, name)
 
 def check(mod):
+    if not mod:
+        output("Could not parse input file")
+        return False
+
     v = Check()
     v.visit(mod)
 
@@ -407,7 +411,8 @@
     try:
         return parser.parse(tokens)
     except ASDLSyntaxError:
-        output(sys.exc_info()[1])
+        err = sys.exc_info()[1]
+        output(str(err))
         lines = buf.split("\n")
         output(lines[err.lineno - 1]) # lines starts at 0, files at 1
 
@@ -424,6 +429,8 @@
     for file in files:
         output(file)
         mod = parse(file)
+        if not mod:
+            break
         output("module", mod.name)
         output(len(mod.dfns), "definitions")
         if not check(mod):