diff --git a/tools/linuxfs/overlay/usr/local/bin/bannerlator-steam-x64 b/tools/linuxfs/overlay/usr/local/bin/bannerlator-steam-x64
index 6971cfa61..479e53a2b 100755
--- a/tools/linuxfs/overlay/usr/local/bin/bannerlator-steam-x64
+++ b/tools/linuxfs/overlay/usr/local/bin/bannerlator-steam-x64
@@ -115,6 +115,10 @@ unset LD_LIBRARY_PATH LD_PRELOAD STEAM_RUNTIME STEAM_RUNTIME_PREFER_HOST_LIBRARI
 # Steam's 32-bit check reports libc.so.6 missing. 64-bit runs either way; proot then answers
 # FEX's path calls itself.
 export PROOT_FP_OFF=1
+# Valve's 64-bit SteamRT3 client (steamrt64/steam), the x86 twin of the arm64 one; steam.sh
+# starts it directly on the beta branch. The legacy ubuntu12_32 path first runs
+# steam-runtime-check-requirements, which refuses without user namespaces - proot has none.
+export STEAM_FORCE_CLIENT=steamrt64
 export HOME=$X64_HOME
 export FEX_ROOTFS=$ROOTFS
 # A FEX process takes its rootfs from FEXServer, not from its own environment, and a server