diff --git a/pkgs/servers/mqtt/mosquitto/default.nix b/pkgs/servers/mqtt/mosquitto/default.nix
index f241f48ac52e..152332538ff9 100644
--- a/pkgs/servers/mqtt/mosquitto/default.nix
+++ b/pkgs/servers/mqtt/mosquitto/default.nix
@@ -17,9 +17,14 @@
 
 let
   # Mosquitto needs external poll enabled in libwebsockets.
-  libwebsockets' = libwebsockets.override {
+  libwebsockets' = (libwebsockets.override {
     withExternalPoll = true;
-  };
+  }).overrideAttrs (old: {
+    # Avoid bug in firefox preventing websockets being created over http/2 connections
+    # https://github.com/eclipse/mosquitto/issues/1211#issuecomment-958137569
+    cmakeFlags = old.cmakeFlags ++ [ "-DLWS_WITH_HTTP2=OFF" ];
+  });
+
 in
 stdenv.mkDerivation rec {
   pname = "mosquitto";