diff --git a/build.cfg b/build.cfg
index 814f4e52..4e2e4641 100644
--- a/build.cfg
+++ b/build.cfg
@@ -39,9 +39,11 @@ CLAWDIE_REF="${CLAWDIE_REF:-main}"
 DEFAULT_PKG_BRANCH="latest"     # latest or quarterly
 DEFAULT_DESKTOP="xfce"          # operator USB desktop
 
-# GPU driver variant (set at build time via --gpu-driver flag)
+# GPU driver variant (set at build time via the GPU_DRIVER environment variable)
 # intel | amd | nvidia-590 | nvidia-470 | nvidia-390 | vesa | "" (auto-detect)
-GPU_DRIVER=""
+# Use the :- form so an env value (e.g. `GPU_DRIVER=nvidia-590 ./build.sh`) is
+# honored; a plain GPU_DRIVER="" here would clobber the environment.
+GPU_DRIVER="${GPU_DRIVER:-}"
 
 # Universal NVIDIA lane (opt-in). When YES, the image carries an on-image NVIDIA
 # pkg repo for all three branches (390/470/580), does NOT bake a single branch,