diff --git a/lib/alloca86_64.S b/lib/alloca86_64.S
index 2a70c26e..8f89fe48 100644
--- a/lib/alloca86_64.S
+++ b/lib/alloca86_64.S
@@ -27,7 +27,9 @@ p2:
 
     sub     %rax,%rsp
     mov     %rsp,%rax
+#ifdef _WIN32
     add     $32,%rax
+#endif
 p3:
     push    %rdx
     ret