diff --git a/src/rt/arch/i386/morestack.S b/src/rt/arch/i386/morestack.S
index 2295957bfaa..f888373e5cf 100644
--- a/src/rt/arch/i386/morestack.S
+++ b/src/rt/arch/i386/morestack.S
@@ -74,7 +74,7 @@ MORESTACK:
     testl %eax,%eax
     jz .L$bail
 
-    movl $12, (%esp)
+    movl $16, (%esp)
     calll UPCALL_ALLOC_C_STACK
     movl %eax,%edx