diff --git a/shared/editor/lib/code.test.ts b/shared/editor/lib/code.test.ts
index 1764ef4ac4..8d60da26e4 100644
--- a/shared/editor/lib/code.test.ts
+++ b/shared/editor/lib/code.test.ts
@@ -1,4 +1,11 @@
-import { getRefractorLangForLanguage, getLabelForLanguage } from "./code";
+import Storage from "../../utils/Storage";
+import {
+  getRefractorLangForLanguage,
+  getLabelForLanguage,
+  setRecentlyUsedCodeLanguage,
+  getRecentlyUsedCodeLanguage,
+  getFrequentCodeLanguages,
+} from "./code";
 
 describe("getRefractorLangForLanguage", () => {
   it("should return the correct lang identifier for a given language", () => {
@@ -26,3 +33,46 @@ describe("getLabelForLanguage", () => {
     expect(getLabelForLanguage("")).toBe("Plain text");
   });
 });
+
+describe("setRecentlyUsedCodeLanguage", () => {
+  beforeEach(() => {
+    Storage.clear();
+  });
+
+  it("should remember the last selected code language", () => {
+    setRecentlyUsedCodeLanguage("javascript");
+    expect(getRecentlyUsedCodeLanguage()).toBe("javascript");
+  });
+
+  it("should not remember mermaid as the last selected code language", () => {
+    setRecentlyUsedCodeLanguage("javascript");
+    setRecentlyUsedCodeLanguage("mermaid");
+    expect(getRecentlyUsedCodeLanguage()).toBe("javascript");
+  });
+
+  it("should not remember mermaidjs as the last selected code language", () => {
+    setRecentlyUsedCodeLanguage("javascript");
+    setRecentlyUsedCodeLanguage("mermaidjs");
+    expect(getRecentlyUsedCodeLanguage()).toBe("javascript");
+  });
+
+  it("should ignore mermaid that was already persisted", () => {
+    Storage.set("rme-code-language", "mermaid");
+    expect(getRecentlyUsedCodeLanguage()).toBeUndefined();
+  });
+});
+
+describe("getFrequentCodeLanguages", () => {
+  beforeEach(() => {
+    Storage.clear();
+  });
+
+  it("should exclude mermaid that was already persisted", () => {
+    Storage.set("frequent-code-languages", {
+      javascript: 3,
+      mermaid: 5,
+      mermaidjs: 2,
+    });
+    expect(getFrequentCodeLanguages()).toEqual(["javascript"]);
+  });
+});
diff --git a/shared/editor/lib/code.ts b/shared/editor/lib/code.ts
index 9e56ccca09..4e09076115 100644
--- a/shared/editor/lib/code.ts
+++ b/shared/editor/lib/code.ts
@@ -374,12 +374,23 @@ export const getRefractorLangForLanguage = (
 export const getLoaderForLanguage = (language: string) =>
   codeLanguages[language as keyof typeof codeLanguages]?.loader;
 
+// Mermaid diagrams have a separate insertion entry point, so they should never
+// be remembered as a recently or frequently used code language.
+const nonPersistableLanguages = ["mermaid", "mermaidjs"];
+
+const isPersistableCodeLanguage = (language: string) =>
+  !nonPersistableLanguages.includes(language);
+
 /**
  * Set the most recent code language used.
  *
  * @param language The language identifier.
  */
 export const setRecentlyUsedCodeLanguage = (language: string) => {
+  if (!isPersistableCodeLanguage(language)) {
+    return;
+  }
+
   const frequentLangs = (Storage.get(StorageKey) ?? {}) as Record<
     string,
     number
@@ -416,8 +427,12 @@ export const setRecentlyUsedCodeLanguage = (language: string) => {
  *
  * @returns The most recent code language used, or undefined if none is set.
  */
-export const getRecentlyUsedCodeLanguage = () =>
-  Storage.get(RecentlyUsedStorageKey) as keyof typeof codeLanguages | undefined;
+export const getRecentlyUsedCodeLanguage = () => {
+  const language = Storage.get(RecentlyUsedStorageKey) as
+    | keyof typeof codeLanguages
+    | undefined;
+  return language && isPersistableCodeLanguage(language) ? language : undefined;
+};
 
 /**
  * Get the most frequent code languages used.
@@ -425,17 +440,20 @@ export const getRecentlyUsedCodeLanguage = () =>
  * @returns An array of the most frequent code languages used.
  */
 export const getFrequentCodeLanguages = () => {
-  const recentLang = Storage.get(RecentlyUsedStorageKey);
-  const frequentLangEntries = Object.entries(Storage.get(StorageKey) ?? {}) as [
-    keyof typeof codeLanguages,
-    number,
-  ][];
+  const recentLang = getRecentlyUsedCodeLanguage();
+  const frequentLangEntries = (
+    Object.entries(Storage.get(StorageKey) ?? {}) as [
+      keyof typeof codeLanguages,
+      number,
+    ][]
+  ).filter(([lang]) => isPersistableCodeLanguage(lang));
 
   const frequentLangs = sortFrequencies(frequentLangEntries)
     .slice(0, frequentLanguagesToGet)
     .map(([lang]) => lang);
 
-  const isRecentLangPresent = frequentLangs.includes(recentLang);
+  const isRecentLangPresent =
+    !!recentLang && frequentLangs.includes(recentLang);
   if (recentLang && !isRecentLangPresent) {
     frequentLangs.pop();
     frequentLangs.push(recentLang);