diff --git a/modules/programs/zsh/default.nix b/modules/programs/zsh/default.nix
index c7ff47c49..d3b2f5c65 100644
--- a/modules/programs/zsh/default.nix
+++ b/modules/programs/zsh/default.nix
@@ -117,6 +117,9 @@ in
 
   config = mkIf cfg.enable {
 
+    warnings = mkIf (cfg.enableFastSyntaxHighlighting && cfg.enableSyntaxHighlighting) [
+      "zsh-fast-syntax-highlighting and zsh-syntax-highlighting are mutually exclusive. Disable one of them."
+    ];
     environment.systemPackages =
       [ # Include zsh package
         pkgs.zsh