diff --git a/public/app/plugins/datasource/alertmanager/ConfigEditor.tsx b/public/app/plugins/datasource/alertmanager/ConfigEditor.tsx
index a457f3dc8cf..817324ebf1b 100644
--- a/public/app/plugins/datasource/alertmanager/ConfigEditor.tsx
+++ b/public/app/plugins/datasource/alertmanager/ConfigEditor.tsx
@@ -1,5 +1,5 @@
 import { produce } from 'immer';
-import React from 'react';
+import React, { useEffect } from 'react';
 import { Link } from 'react-router-dom';
 
 import { SIGV4ConnectionConfig } from '@grafana/aws-sdk';
@@ -33,6 +33,17 @@ const IMPL_OPTIONS: Array<SelectableValue<AlertManagerImplementation>> = [
 export const ConfigEditor = (props: Props) => {
   const { options, onOptionsChange } = props;
 
+  // As we default to Mimir, we need to make sure the implementation is set from the start
+  useEffect(() => {
+    if (!options.jsonData.implementation) {
+      onOptionsChange(
+        produce(options, (draft) => {
+          draft.jsonData.implementation = AlertManagerImplementation.mimir;
+        })
+      );
+    }
+  }, [options, onOptionsChange]);
+
   return (
     <>
       <h3 className="page-heading">Alertmanager</h3>