diff --git a/src/cmd/compile/internal/devirtualize/devirtualize.go b/src/cmd/compile/internal/devirtualize/devirtualize.go
index dfcdd42236d..cb4608a0246 100644
--- a/src/cmd/compile/internal/devirtualize/devirtualize.go
+++ b/src/cmd/compile/internal/devirtualize/devirtualize.go
@@ -387,6 +387,9 @@ func (s *State) assignments(n *ir.Name) []assignment {
 	if fun == nil {
 		base.FatalfAt(n.Pos(), "n.Curfn = <nil>")
 	}
+	if n.Class != ir.PAUTO {
+		base.FatalfAt(n.Pos(), "n.Class = %v; want = PAUTO", n.Class)
+	}
 
 	if !n.Type().IsInterface() {
 		base.FatalfAt(n.Pos(), "name passed to assignments is not of an interface type: %v", n.Type())
@@ -432,6 +435,9 @@ func (s *State) analyze(nodes ir.Nodes) {
 		if n.Op() != ir.ONAME {
 			base.FatalfAt(n.Pos(), "n.Op = %v; want = ONAME", n.Op())
 		}
+		if n.Class != ir.PAUTO {
+			return nil, -1
+		}
 
 		switch a := assignment.(type) {
 		case nil: