diff --git a/src/cmd/6l/pass.c b/src/cmd/6l/pass.c
index a2a82a18b5f..8dc0ed551b6 100644
--- a/src/cmd/6l/pass.c
+++ b/src/cmd/6l/pass.c
@@ -469,7 +469,7 @@ dostkoff(void)
 
 			/* 160 comes from 3 calls (3*8) 4 safes (4*8) and 104 guard */
 			moreconst1 = 0;
-			if(autoffset+160 > 4096)
+			if(autoffset+160+textarg > 4096)
 				moreconst1 = (autoffset+160) & ~7LL;
 			moreconst2 = textarg;
 
diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index d898b30b37d..b07b6d67c4d 100644
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -749,6 +749,8 @@ newstack(void)
 	args = m->moreargs;
 	g1 = m->curg;
 
+	if(m->morebuf.sp < g1->stackguard - StackGuard)
+		throw("split stack overflow");
 
 	if(frame == 1 && args > 0 && m->morebuf.sp - sizeof(Stktop) - args - 32 > g1->stackguard) {
 		// special case: called from reflect.call (frame == 1)