diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 9ed4a233..cd6789b0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -204,6 +204,10 @@ jobs:
           need=""
           command -v cmake >/dev/null || need="$need cmake"
           command -v clang >/dev/null || need="$need clang"
+          # aarch64 的 libc 头（1.7MB，仅头文件，**不含编译器**）。
+          # 用它 + 已预装的 clang 交叉前端，替代 10MB+ 的完整交叉 GCC
+          # （实测那个会卡在下载 cpp-13-aarch64，180s 超时）。
+          [ -d /usr/aarch64-linux-gnu/include ] || need="$need libc6-dev-arm64-cross"
 
           if [ -z "$need" ]; then
             echo "✅ 依赖已存在，跳过 apt-get：$(command -v cmake clang | tr '\n' ' ')"
diff --git a/Makefile b/Makefile
index 6b00f6b3..63970525 100644
--- a/Makefile
+++ b/Makefile
@@ -295,10 +295,15 @@ csrc-cross:
 		echo "  [SKIP] 无 clang、无 aarch64-linux-gnu-gcc（未装任何交叉前端）"; exit 0; \
 	fi; \
 	\
+	ARM64_SYSINC=""; \
+	for d in /usr/aarch64-linux-gnu/include /usr/include/aarch64-linux-gnu; do \
+		[ -d "$$d" ] && ARM64_SYSINC="$$ARM64_SYSINC -isystem $$d"; \
+	done; \
+	\
 	if [ "$$MODE" = "clang-target" ]; then \
-		printf 'int main(void){return 0;}\n' > /tmp/_archchk.c; \
-		if ! clang --target=aarch64-linux-gnu -fsyntax-only /tmp/_archchk.c 2>/dev/null; then \
-			echo "  [SKIP] clang 不支持 --target=aarch64-linux-gnu（版本过旧）"; exit 0; \
+		printf '#include <string.h>\nint main(void){return 0;}\n' > /tmp/_archchk.c; \
+		if ! clang --target=aarch64-linux-gnu $$ARM64_SYSINC -fsyntax-only /tmp/_archchk.c >/dev/null 2>&1; then \
+			echo "  [SKIP] clang 交叉前端不可用（缺 aarch64 libc 头，装 libc6-dev-arm64-cross 即可）"; exit 0; \
 		fi; \
 	fi; \
 	\