diff --git a/docs/danger.md b/docs/danger.md
index 19728f00e9..acf14018e6 100644
--- a/docs/danger.md
+++ b/docs/danger.md
@@ -23,6 +23,7 @@ Here are the checks that Danger does so far:
 - PR description is not empty
 - Big PR got a warning to recommend to split
 - PR contains a file for towncrier and extension is checked
+- PR does not modify frozen classes
 - PR contains a Sign-Off, with exception for Element employee contributors
 - PR with change on layout should include screenshot in the description
 - PR which adds png file warn about the usage of vector drawables
diff --git a/tools/danger/dangerfile.js b/tools/danger/dangerfile.js
index 4efd236419..c7db52fa19 100644
--- a/tools/danger/dangerfile.js
+++ b/tools/danger/dangerfile.js
@@ -52,6 +52,19 @@ if (requiresChangelog) {
     }
 }
 
+// check that frozen classes have not been modified
+const frozenClasses = [
+    "OlmInboundGroupSessionWrapper.kt",
+    "OlmInboundGroupSessionWrapper2.kt",
+]
+
+frozenClasses.forEach(frozen => {
+    if (editedFiles.some(file => file.endsWith(frozen))) {
+        fail("Frozen class `" + frozen + "` has been modified. Please do not modify frozen class.")
+    }
+  }
+)
+
 // Check for a sign-off
 const signOff = "Signed-off-by:"