diff --git a/pkgs/applications/window-managers/fluxbox/default.nix b/pkgs/applications/window-managers/fluxbox/default.nix
index 36a22cb46d76..934f8c9b3fc2 100644
--- a/pkgs/applications/window-managers/fluxbox/default.nix
+++ b/pkgs/applications/window-managers/fluxbox/default.nix
@@ -15,6 +15,15 @@ stdenv.mkDerivation rec {
     sha256 = "1h1f70y40qd225dqx937vzb4k2cz219agm1zvnjxakn5jkz7b37w";
   };
 
+  patches = [
+    # Upstream fix to build against gcc-11.
+    (fetchurl {
+      name = "gcc-11.patch";
+      url = "http://git.fluxbox.org/fluxbox.git/patch/?id=22866c4d30f5b289c429c5ca88d800200db4fc4f";
+      sha256 = "1x7126rlmzky51lk370fczssgnjs7i6wgfaikfib9pvn4vv945ai";
+    })
+  ];
+
   nativeBuildInputs = [ pkg-config ];
 
   buildInputs = [ freetype fribidi libXext libXft libXpm libXrandr libXrender xorgproto libXinerama imlib2 ];