diff --git a/iso/builder/build-nvidia-module.sh b/iso/builder/build-nvidia-module.sh
index b122dc4..df3f837 100644
--- a/iso/builder/build-nvidia-module.sh
+++ b/iso/builder/build-nvidia-module.sh
@@ -84,9 +84,15 @@ done
 echo "kernel source: $KERNEL_SRC"
 
 # Build kernel modules
+# CFLAGS_MODULE: add GCC include dir so NVIDIA's nv_stdarg.h can find stdarg.h.
+# Kernel build uses -nostdinc which strips GCC's own includes; we restore it here.
+GCC_INCLUDES=$(gcc --print-file-name=include 2>/dev/null || echo "")
 echo "=== building kernel modules ($(nproc) cores) ==="
 cd "$KERNEL_SRC"
-make -j$(nproc) KERNEL_UNAME="$KVER" SYSSRC="$KDIR" modules 2>&1 | tail -5
+make -j$(nproc) \
+    KERNEL_UNAME="$KVER" SYSSRC="$KDIR" \
+    ${GCC_INCLUDES:+CFLAGS_MODULE="-I${GCC_INCLUDES}"} \
+    modules 2>&1 | tail -10
 
 # Collect outputs
 mkdir -p "$CACHE_DIR/modules" "$CACHE_DIR/bin" "$CACHE_DIR/lib"