diff --git a/lib/solargraph/diagnostics/rubocop.rb b/lib/solargraph/diagnostics/rubocop.rb
index cfeca4fb3..f8e6c90da 100644
--- a/lib/solargraph/diagnostics/rubocop.rb
+++ b/lib/solargraph/diagnostics/rubocop.rb
@@ -32,7 +32,7 @@ def diagnose source, _api_map
       rescue RuboCop::ValidationError, RuboCop::ConfigNotFoundError => e
         raise DiagnosticsError, "Error in RuboCop configuration: #{e.message}"
       rescue JSON::ParserError
-        raise DiagnosticsError, 'RuboCop returned invalid data'
+        raise DiagnosticsError, "RuboCop returned invalid data: #{e.message}"
       end
 
       private