diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 6ff50bf0..874992da 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -31,7 +31,11 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - name: make & test tcc (aarch64-osx)
-      run: ./configure && make && make test -k
+      run: |
+        ./configure
+        make
+        make test -k
+        make -C tests/tests2 tests2.133
 
   test-x86_64-win32:
     runs-on: windows-2025
@@ -63,6 +67,22 @@ jobs:
         .\tcc -I.. libtcc.dll -v ../tests/libtcc_test.c -o libtest.exe && .\libtest.exe
         .\tcc -I.. libtcc.dll -run ../tests/libtcc_test.c
 
+  test-x86_64-win32-clang64:
+    runs-on: windows-2025
+    timeout-minutes: 6
+    steps:
+    - uses: actions/checkout@v4
+    - name: make & test tcc (x86_64-win32-clang64)
+      shell: cmd
+      run: |
+        echo ::group:: setup msys clang64
+        set MSYS2_PATH_TYPE=inherit
+        set MSYSTEM=CLANG64
+        set CHERE_INVOKING=yes
+        C:\msys64\usr\bin\bash -l -c "pacman -S --noconfirm mingw-w64-clang-x86_64-clang"
+        echo ::endgroup::
+        C:\msys64\usr\bin\bash -l -c "./configure --cc=clang && make && make -C tests test3"
+
   test-i386-win32:
     runs-on: windows-2025
     timeout-minutes: 6
diff --git a/arm64-gen.c b/arm64-gen.c
index 37eddbdf..438a2205 100644
--- a/arm64-gen.c
+++ b/arm64-gen.c
@@ -862,6 +862,13 @@ static unsigned long arm64_pcs_aux(int variadic, int n, CType **type, unsigned l
     unsigned long ns = 32; // next stack offset
     int i;
 
+#if defined(TCC_TARGET_MACHO)
+    /* Old-style / unprototyped calls must follow the variadic stack rules
+       from the first argument on Darwin. */
+    if (variadic < 0)
+        nx = 8, nv = 8;
+#endif
+
     for (i = 0; i < n; i++) {
         int hfa = arm64_hfa(type[i], 0);
         int win_vararg_float = 0;
diff --git a/lib/bt-exe.c b/lib/bt-exe.c
index 6f083173..6542bfd0 100644
--- a/lib/bt-exe.c
+++ b/lib/bt-exe.c
@@ -63,25 +63,6 @@ void __bt_init(rt_context *p, int is_exe)
 }
 
 #ifdef _WIN32
-static const char *bt_backtrace_format(const char *fmt, char *skip, int *one)
-{
-    const char *a, *b;
-
-    skip[0] = 0;
-    if (fmt[0] == '^' && (b = strchr(a = fmt + 1, fmt[0]))) {
-        size_t len = b - a;
-        if (len >= 40)
-            len = 39;
-        memcpy(skip, a, len);
-        skip[len] = 0;
-        fmt = b + 1;
-    }
-    *one = 0;
-    if (fmt[0] == '\001')
-        ++fmt, *one = 1;
-    return fmt;
-}
-
 static int bt_backtrace_msg(rt_frame *f, const char *fmt, const char *msg)
 {
     rt_context *rc, *rc2;
@@ -92,7 +73,7 @@ static int bt_backtrace_msg(rt_frame *f, const char *fmt, const char *msg)
     bt_info bi;
     addr_t (*getinfo)(rt_context*, addr_t, bt_info*);
 
-    bt_backtrace_format(fmt, skip, &one);
+    rt_backtrace_format(fmt, skip, &one);
 
     rt_wait_sem();
     rc = g_rc;
diff --git a/tccrun.c b/tccrun.c
index 01f40f32..1b19dd78 100644
--- a/tccrun.c
+++ b/tccrun.c
@@ -730,6 +730,25 @@ static int rt_printf(const char *fmt, ...)
     return r;
 }
 
+static const char *rt_backtrace_format(const char *fmt, char *skip, int *one)
+{
+    const char *a, *b;
+
+    skip[0] = 0;
+    if (fmt[0] == '^' && (b = strchr(a = fmt + 1, fmt[0]))) {
+        size_t len = b - a;
+        if (len >= 40)
+            len = 39;
+        memcpy(skip, a, len);
+        skip[len] = 0;
+        fmt = b + 1;
+    }
+    *one = 0;
+    if (fmt[0] == '\001')
+        ++fmt, *one = 1;
+    return fmt;
+}
+
 static char *rt_elfsym(rt_context *rc, addr_t wanted_pc, addr_t *func_addr)
 {
     ElfW(Sym) *esym;
@@ -1168,20 +1187,11 @@ int _tcc_backtrace(rt_frame *f, const char *fmt, va_list ap)
     addr_t pc;
     char skip[40], msg[200];
     int i, level, ret, n, one;
-    const char *a, *b;
+    const char *a;
     bt_info bi;
     addr_t (*getinfo)(rt_context*, addr_t, bt_info*);
 
-    skip[0] = 0;
-    /* If fmt is like "^file.c^..." then skip calls from 'file.c' */
-    if (fmt[0] == '^' && (b = strchr(a = fmt + 1, fmt[0]))) {
-        memcpy(skip, a, b - a), skip[b - a] = 0;
-        fmt = b + 1;
-    }
-    one = 0;
-    /* hack for bcheck.c:dprintf(): one level, no newline */
-    if (fmt[0] == '\001')
-        ++fmt, one = 1;
+    fmt = rt_backtrace_format(fmt, skip, &one);
     vsnprintf(msg, sizeof msg, fmt, ap);
 
     rt_wait_sem();
diff --git a/tests/Makefile b/tests/Makefile
index e8656c40..c466295a 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -77,7 +77,7 @@ endif
 TCCTEST_REF = test.ref
 ifeq ($(ARCH)-$(TARGETOS),arm64-WIN32)
 TCCTEST_REF = test.ref.win32-arm64
-else ifeq ($(ARCH)-$(TARGETOS)-$(HOST_WIN_UCRT),x86_64-WIN32-yes)
+else ifeq ($(ARCH)-$(TARGETOS)-$(CC_NAME)-$(HOST_WIN_UCRT),x86_64-WIN32-clang-yes)
 # CLANG64/UCRT generates a different host reference than the msvcrt-backed TCC runtime.
 TCCTEST_REF = test.ref.win32-x86_64-ucrt
 endif
diff --git a/tests/tests2/112_backtrace.c b/tests/tests2/112_backtrace.c
index 0b596d08..2b5bd4cd 100644
--- a/tests/tests2/112_backtrace.c
+++ b/tests/tests2/112_backtrace.c
@@ -61,7 +61,7 @@ void f2()
 void f1()
 {
     printf("* f1()\n"), fflush(stdout);
-    tcc_backtrace("Hello from %s!", "f1");
+    tcc_backtrace("^12345678901234567890123456789012345678901234567890^Hello from %s!", "f1");
     f2();
 }
 int main(int argc, char **argv)