diff --git a/tools/linter_lib/custom_check.py b/tools/linter_lib/custom_check.py
index 4c4ee5a113..9c427271da 100644
--- a/tools/linter_lib/custom_check.py
+++ b/tools/linter_lib/custom_check.py
@@ -802,7 +802,7 @@ def build_custom_checkers(by_lang):
          'strip': '\n',
          'exclude': set(['zerver/webhooks/']),
          'description': 'Fix tab-based whitespace'},
-        {'pattern': r':["\[\{]',
+        {'pattern': r'":["\[\{]',
          'exclude': set(['zerver/webhooks/', 'zerver/tests/fixtures/']),
          'description': 'Require space after : in JSON'},
     ]  # type: RuleList