diff --git a/pkg/apis/pipeline/v1alpha1/run_validation.go b/pkg/apis/pipeline/v1alpha1/run_validation.go
index 8ad179c85b4..2a617e4a554 100644
--- a/pkg/apis/pipeline/v1alpha1/run_validation.go
+++ b/pkg/apis/pipeline/v1alpha1/run_validation.go
@@ -44,6 +44,9 @@ func (rs *RunSpec) Validate(ctx context.Context) *apis.FieldError {
 	if rs.Ref != nil && rs.Spec != nil {
 		return apis.ErrMultipleOneOf("spec.ref", "spec.spec")
 	}
+	if rs.Ref == nil && rs.Spec == nil {
+		return apis.ErrMissingOneOf("spec.ref", "spec.spec")
+	}
 	if rs.Ref != nil {
 		if rs.Ref.APIVersion == "" {
 			return apis.ErrMissingField("spec.ref.apiVersion")
diff --git a/pkg/apis/pipeline/v1alpha1/run_validation_test.go b/pkg/apis/pipeline/v1alpha1/run_validation_test.go
index 15c79d1505b..b174004d637 100644
--- a/pkg/apis/pipeline/v1alpha1/run_validation_test.go
+++ b/pkg/apis/pipeline/v1alpha1/run_validation_test.go
@@ -45,16 +45,26 @@ func TestRun_Invalid(t *testing.T) {
 		want: apis.ErrMissingField("spec"),
 	}, {
 		name: "Empty spec",
+		run: &v1alpha1.Run{
+			ObjectMeta: metav1.ObjectMeta{
+				Name: "temp",
+			},
+			Spec: v1alpha1.RunSpec{},
+		},
+		want: apis.ErrMissingField("spec"),
+	}, {
+		name: "Both spec and ref missing",
 		run: &v1alpha1.Run{
 			ObjectMeta: metav1.ObjectMeta{
 				Name: "temp",
 			},
 			Spec: v1alpha1.RunSpec{
-				Ref:  nil,
-				Spec: nil,
+				Ref:                nil,
+				Spec:               nil,
+				ServiceAccountName: "test-sa",
 			},
 		},
-		want: apis.ErrMissingField("spec"),
+		want: apis.ErrMissingOneOf("spec.ref", "spec.spec"),
 	}, {
 		name: "Both Ref and Spec",
 		run: &v1alpha1.Run{