diff --git a/testing/web-platform/tests/tools/wptrunner/wptrunner/wptmanifest/parser.py b/testing/web-platform/tests/tools/wptrunner/wptrunner/wptmanifest/parser.py
index fa2ae30a0976..9e0ff029b847 100644
--- a/testing/web-platform/tests/tools/wptrunner/wptrunner/wptmanifest/parser.py
+++ b/testing/web-platform/tests/tools/wptrunner/wptrunner/wptmanifest/parser.py
@@ -555,7 +555,8 @@ class Parser(object):
         while self.token == (token_types.paren, "["):
             self.consume()
             if self.token[0] != token_types.string:
-                raise ParseError
+                raise ParseError(self.tokenizer.filename, self.tokenizer.line_number,
+                                 "Token '{}' is not a string".format(self.token[0]))
             self.tree.append(DataNode(self.token[1]))
             self.consume()
             self.expect(token_types.paren, "]")
@@ -584,7 +585,8 @@ class Parser(object):
         elif self.token[0] == token_types.atom:
             self.atom()
         else:
-            raise ParseError
+            raise ParseError(self.tokenizer.filename, self.tokenizer.line_number,
+                             "Token '{}' is not a known type".format(self.token[0]))
 
     def list_value(self):
         self.tree.append(ListNode())