diff --git a/src/pkg/go/ast/walk.go b/src/pkg/go/ast/walk.go
index 66b1dc2499..fef2503c37 100644
--- a/src/pkg/go/ast/walk.go
+++ b/src/pkg/go/ast/walk.go
@@ -158,7 +158,9 @@ func Walk(v Visitor, node Node) {
 		Walk(v, n.Fields)
 
 	case *FuncType:
-		Walk(v, n.Params)
+		if n.Params != nil {
+			Walk(v, n.Params)
+		}
 		if n.Results != nil {
 			Walk(v, n.Results)
 		}