diff --git a/api/krusty/blankvalues_test.go b/api/krusty/blankvalues_test.go
new file mode 100644
index 000000000..dfba4f365
--- /dev/null
+++ b/api/krusty/blankvalues_test.go
@@ -0,0 +1,49 @@
+package krusty_test
+
+import (
+	"strings"
+	"testing"
+
+	kusttest_test "sigs.k8s.io/kustomize/api/testutils/kusttest"
+)
+
+// test for https://github.com/kubernetes-sigs/kustomize/issues/4240
+func TestBlankNamespace4240(t *testing.T) {
+	th := kusttest_test.MakeHarness(t)
+	th.WriteK(".", `
+resources:
+- resource.yaml
+`)
+
+	th.WriteF("resource.yaml", `
+---
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: test
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: Role
+metadata:
+  name: test
+rules: []
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: RoleBinding
+metadata:
+  name: test
+subjects:
+- kind: ServiceAccount
+  name: test
+  namespace:
+roleRef:
+  kind: Role
+  name: test
+  apiGroup: rbac.authorization.k8s.io	
+`)
+
+	err := th.RunWithErr(".", th.MakeDefaultOptions())
+	if !strings.Contains(err.Error(), "Invalid Input: namespace is blank for resource") {
+		t.Fatalf("unexpected error: %q", err)
+	}
+}
diff --git a/api/resmap/reswrangler.go b/api/resmap/reswrangler.go
index 93d82e64d..8b8d7834b 100644
--- a/api/resmap/reswrangler.go
+++ b/api/resmap/reswrangler.go
@@ -442,7 +442,7 @@ func getNamespacesForRoleBinding(r *resource.Resource) (map[string]bool, error)
 					if n, ok3 := ns.(string); ok3 {
 						result[n] = true
 					} else {
-						return nil, errors.New("Invalid Input: namespace is blank")
+						return nil, errors.New(fmt.Sprintf("Invalid Input: namespace is blank for resource %q\n", r.CurId()))
 					}
 				}
 			}