diff --git a/README.md b/README.md
index c87a7aa7..e458f34f 100644
--- a/README.md
+++ b/README.md
@@ -431,6 +431,10 @@ Do not add `-dUNICODERTL` or reuse the application's `.mooncompiler` profile
 when building the IDE/LCL. These select different string ABIs; adding a define
 to the Lazarus command line cannot change an already compiled RTL.
 
+Under WSLg, `./lazarus` selects the GTK X11 backend (Xwayland) unless
+`GDK_BACKEND` is already set: the WSLg compositor crashes when a window that has
+a transient child is destroyed, and the IDE does this on its first run.
+
 Since 2.5.2, the IDE profile preserves the FPC `TStringList` insertion hooks used
 by Lazarus subclasses. The Unicode application profile retains the Delphi
 insertion contract. Both profiles are checked independently in CI.
diff --git a/lazarus b/lazarus
index 1e840630..10e73684 100755
--- a/lazarus
+++ b/lazarus
@@ -16,4 +16,9 @@ export PP="$IDE_FPC"
 export PPC_CONFIG_PATH="$IDE_TOOLCHAIN/etc"
 export LAZARUSDIR="$LAZARUS_SOURCE"
 unset FPCDIR
+# The WSLg compositor crashes when a window that has a transient child is
+# destroyed, which the IDE does on its first run; Xwayland is not affected.
+if [[ -z ${GDK_BACKEND-} && -d /mnt/wslg ]]; then
+  export GDK_BACKEND=x11
+fi
 exec "$LAZARUS_EXE" "--pcp=$PRIMARY_CONFIG" "$@"