diff --git a/pkgs/applications/editors/emacs-modes/cedet/default.nix b/pkgs/applications/editors/emacs-modes/cedet/default.nix
index e350dc08e71..5fbe095c4f3 100644
--- a/pkgs/applications/editors/emacs-modes/cedet/default.nix
+++ b/pkgs/applications/editors/emacs-modes/cedet/default.nix
@@ -44,5 +44,8 @@ stdenv.mkDerivation rec {
     license = stdenv.lib.licenses.gpl2Plus;
 
     homepage = http://cedet.sourceforge.net/;
+
+    # Fails with `semantic-idle.el:42:1:Error: Invalid function: class-p`
+    broken = true;
   };
 }