diff --git a/public/app/plugins/datasource/prometheus/components/monaco-query-field/MonacoQueryField.tsx b/public/app/plugins/datasource/prometheus/components/monaco-query-field/MonacoQueryField.tsx
index a16e5393283..03db833c858 100644
--- a/public/app/plugins/datasource/prometheus/components/monaco-query-field/MonacoQueryField.tsx
+++ b/public/app/plugins/datasource/prometheus/components/monaco-query-field/MonacoQueryField.tsx
@@ -1,5 +1,5 @@
-import React, { useRef } from 'react';
-import { CodeEditor, CodeEditorMonacoOptions } from '@grafana/ui';
+import React, { useRef, useEffect } from 'react';
+import { CodeEditor, CodeEditorMonacoOptions, Monaco, monacoTypes } from '@grafana/ui';
 import { useLatest } from 'react-use';
 import { promLanguageDefinition } from 'monaco-promql';
 import { getCompletionProvider } from './monaco-completion-provider';
@@ -22,6 +22,24 @@ const options: CodeEditorMonacoOptions = {
   fixedOverflowWidgets: true,
 };
 
+const PROMQL_LANG_ID = promLanguageDefinition.id;
+
+// we must only run the promql-setup code once
+let PROMQL_SETUP_STARTED = false;
+
+function ensurePromQL(monaco: Monaco) {
+  if (PROMQL_SETUP_STARTED === false) {
+    PROMQL_SETUP_STARTED = true;
+    const { aliases, extensions, mimetypes, loader } = promLanguageDefinition;
+    monaco.languages.register({ id: PROMQL_LANG_ID, aliases, extensions, mimetypes });
+
+    loader().then((mod) => {
+      monaco.languages.setMonarchTokensProvider(PROMQL_LANG_ID, mod.language);
+      monaco.languages.setLanguageConfiguration(PROMQL_LANG_ID, mod.languageConfiguration);
+    });
+  }
+}
+
 const MonacoQueryField = (props: Props) => {
   const containerRef = useRef<HTMLDivElement>(null);
   const { languageProvider, history, onChange, initialValue } = props;
@@ -29,6 +47,15 @@ const MonacoQueryField = (props: Props) => {
   const lpRef = useLatest(languageProvider);
   const historyRef = useLatest(history);
 
+  const autocompleteDisposeFun = useRef<(() => void) | null>(null);
+
+  useEffect(() => {
+    // when we unmount, we unregister the autocomplete-function, if it was registered
+    return () => {
+      autocompleteDisposeFun.current?.();
+    };
+  }, []);
+
   return (
     <div
       // NOTE: we will be setting inline-style-width/height on this element
@@ -48,7 +75,8 @@ const MonacoQueryField = (props: Props) => {
         monacoOptions={options}
         language="promql"
         value={initialValue}
-        onBeforeEditorMount={(monaco) => {
+        onBeforeEditorMount={ensurePromQL}
+        onEditorDidMount={(editor, monaco) => {
           // we construct a DataProvider object
           const getSeries = (selector: string) => lpRef.current.getSeries(selector);
 
@@ -69,19 +97,34 @@ const MonacoQueryField = (props: Props) => {
           };
 
           const dataProvider = { getSeries, getHistory, getAllMetricNames };
+          const completionProvider = getCompletionProvider(monaco, dataProvider);
 
-          const langId = promLanguageDefinition.id;
-          monaco.languages.register(promLanguageDefinition);
-          promLanguageDefinition.loader().then((mod) => {
-            monaco.languages.setMonarchTokensProvider(langId, mod.language);
-            monaco.languages.setLanguageConfiguration(langId, mod.languageConfiguration);
-            const completionProvider = getCompletionProvider(monaco, dataProvider);
-            monaco.languages.registerCompletionItemProvider(langId, completionProvider);
-          });
+          // completion-providers in monaco are not registered directly to editor-instances,
+          // they are registerd to languages. this makes it hard for us to have
+          // separate completion-providers for every query-field-instance
+          // (but we need that, because they might connect to different datasources).
+          // the trick we do is, we wrap the callback in a "proxy",
+          // and in the proxy, the first thing is, we check if we are called from
+          // "our editor instance", and if not, we just return nothing. if yes,
+          // we call the completion-provider.
+          const filteringCompletionProvider: monacoTypes.languages.CompletionItemProvider = {
+            ...completionProvider,
+            provideCompletionItems: (model, position, context, token) => {
+              // if the model-id does not match, then this call is from a different editor-instance,
+              // not "our instance", so return nothing
+              if (editor.getModel()?.id !== model.id) {
+                return { suggestions: [] };
+              }
+              return completionProvider.provideCompletionItems(model, position, context, token);
+            },
+          };
 
-          // FIXME: should we unregister this at end end?
-        }}
-        onEditorDidMount={(editor, monaco) => {
+          const { dispose } = monaco.languages.registerCompletionItemProvider(
+            PROMQL_LANG_ID,
+            filteringCompletionProvider
+          );
+
+          autocompleteDisposeFun.current = dispose;
           // this code makes the editor resize itself so that the content fits
           // (it will grow taller when necessary)
           // FIXME: maybe move this functionality into CodeEditor, like: