diff --git a/pkgs/build-support/build-fhsenv-bubblewrap/default.nix b/pkgs/build-support/build-fhsenv-bubblewrap/default.nix
index 12f3e7d58552..398a99e80e8c 100644
--- a/pkgs/build-support/build-fhsenv-bubblewrap/default.nix
+++ b/pkgs/build-support/build-fhsenv-bubblewrap/default.nix
@@ -196,8 +196,10 @@ let
     x11_args+=(--tmpfs /tmp/.X11-unix)
 
     # Try to guess X socket path. This doesn't cover _everything_, but it covers some things.
-    if [[ "$DISPLAY" == :* ]]; then
-      display_nr=''${DISPLAY#?}
+    if [[ "$DISPLAY" == *:* ]]; then
+      # recover display number from $DISPLAY formatted [host]:num[.screen]
+      display_nr=''${DISPLAY/#*:} # strip host
+      display_nr=''${display_nr/%.*} # strip screen
       local_socket=/tmp/.X11-unix/X$display_nr
       x11_args+=(--ro-bind-try "$local_socket" "$local_socket")
     fi