diff --git a/packages/grafana-prometheus/src/querybuilder/operationUtils.ts b/packages/grafana-prometheus/src/querybuilder/operationUtils.ts
index a0bda0d598f..bf5bc98c0ad 100644
--- a/packages/grafana-prometheus/src/querybuilder/operationUtils.ts
+++ b/packages/grafana-prometheus/src/querybuilder/operationUtils.ts
@@ -96,8 +96,8 @@ export function rangeRendererLeftWithParams(
 function renderParams(model: QueryBuilderOperation, def: QueryBuilderOperationDef, innerExpr: string) {
   return (model.params ?? []).map((value, index) => {
     const paramDef = def.params[index];
-    if (paramDef.type === 'string') {
-      return '"' + value + '"';
+    if (paramDef?.type === 'string') {
+      return `"${value}"`;
     }
 
     return value;