diff --git a/mk/prefix.mk b/mk/prefix.mk
index 664090a0e1..d8378873cb 100644
--- a/mk/prefix.mk
+++ b/mk/prefix.mk
@@ -493,6 +493,22 @@ endif
 	cp -r "$(CLANG_TARGET)/stage/usr/". "$@.partial"
 	cp -r "$(LLD_TARGET)/stage/usr/". "$@.partial"
 	mv "$@.partial" "$@"
+# Propagate the freshly-built host LLVM (which now carries the AMDGPU + NVPTX GPU
+# backends per recipes/dev/llvm21) into the redoxer toolchain. The Mesa build
+# reads a host llvm-config through bin/x86_64-unknown-redox-llvm-config, which
+# execs $COOKBOOK_HOST_SYSROOT/bin/llvm-config (= this toolchain). The toolchain
+# ships a downloaded X86-only LLVM, so without this sync mesa's
+# dependency('llvm', modules: [... amdgpu ...]) reports amdgpu(missing) and the
+# GPU driver build fails. rsync WITHOUT --delete so the toolchain's gcc/rust and
+# redox-target files are preserved; only the (same-version, 21.1.2) LLVM
+# binaries/libs/headers/cmake are updated to the AMDGPU/NVPTX build.
+	@REDOXER_TC=$(HOME)/.redoxer/$(TARGET)/toolchain; \
+	if [ -d "$$REDOXER_TC/bin" ]; then \
+		rsync -a "$@/bin/llvm-config" "$$REDOXER_TC/bin/llvm-config"; \
+		rsync -a "$@/lib/" "$$REDOXER_TC/lib/"; \
+		rsync -a "$@/include/llvm" "$@/include/llvm-c" "$$REDOXER_TC/include/" 2>/dev/null || true; \
+		echo "  [toolchain] synced AMDGPU/NVPTX host LLVM into redoxer toolchain"; \
+	fi
 # no longer needed, delete build files to save disk space
 	rm -rf $(LLVM_TARGET) $(CLANG_TARGET) $(LLD_TARGET)
 endif