diff --git a/api/krusty/generatormergeandreplace_test.go b/api/krusty/generatormergeandreplace_test.go
index 32407bd30..1b6798502 100644
--- a/api/krusty/generatormergeandreplace_test.go
+++ b/api/krusty/generatormergeandreplace_test.go
@@ -541,7 +541,7 @@ configMapGenerator:
 	if err == nil {
 		t.Fatalf("expected error")
 	}
-	if !strings.Contains(err.Error(), "must merge or replace") {
+	if !strings.Contains(err.Error(), "behavior must be merge or replace") {
 		t.Fatalf("unexpected error %v", err)
 	}
 }
@@ -566,7 +566,7 @@ secretGenerator:
 	if err == nil {
 		t.Fatalf("expected error")
 	}
-	if !strings.Contains(err.Error(), "must merge or replace") {
+	if !strings.Contains(err.Error(), "behavior must be merge or replace") {
 		t.Fatalf("unexpected error %v", err)
 	}
 }
diff --git a/api/resmap/resmap.go b/api/resmap/resmap.go
index 380dbe79d..56b67b181 100644
--- a/api/resmap/resmap.go
+++ b/api/resmap/resmap.go
@@ -691,7 +691,7 @@ func (m *resWrangler) appendReplaceOrMerge(
 			res.Merge(old)
 		default:
 			return fmt.Errorf(
-				"id %#v exists; must merge or replace", id)
+				"id %#v exists; behavior must be merge or replace", id)
 		}
 		i, err := m.Replace(res)
 		if err != nil {