diff --git a/lib/alloca86_64-bt.S b/lib/alloca86_64-bt.S
index 4cbad90f..15bca090 100644
--- a/lib/alloca86_64-bt.S
+++ b/lib/alloca86_64-bt.S
@@ -5,7 +5,6 @@
 __bound_alloca:
 
 #ifdef _WIN32
-    # bound checking is not implemented
     pop     %rdx
     mov     %rcx,%rax
     add     $15,%rax
@@ -23,8 +22,18 @@ p2:
 
     sub     %rax,%rsp
     mov     %rsp,%rax
-    add     $32,%rax
 
+    push    %rdx
+    push    %rax
+    mov     %rcx,%rdx
+    mov     %rax,%rcx
+    sub     $20,%rsp
+    call   __bound_new_region
+    add     $20,%rsp
+    pop     %rax
+    pop     %rdx
+
+    add     $32,%rax
 p3:
     push    %rdx
     ret
diff --git a/x86_64-gen.c b/x86_64-gen.c
index 741ae0ff..e5d99fa7 100644
--- a/x86_64-gen.c
+++ b/x86_64-gen.c
@@ -1025,7 +1025,7 @@ void gfunc_call(int nb_args)
 
     if ((vtop->r & VT_SYM) && vtop->sym->v == TOK_alloca) {
         /* need to add the "func_scratch" area after alloca */
-        o(0x48); func_alloca = oad(0x05, func_alloca); /* sub $NN, %rax */
+        o(0x48); func_alloca = oad(0x2d, func_alloca); /* sub $NN, %rax */
     }
 
     /* other compilers don't clear the upper bits when returning char/short */