diff --git a/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/internal/managedfields.go b/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/internal/managedfields.go
index 652ba64a839..40237cdc660 100644
--- a/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/internal/managedfields.go
+++ b/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/internal/managedfields.go
@@ -101,6 +101,14 @@ func DecodeManagedFields(encodedManagedFields []metav1.ManagedFieldsEntry) (Mana
 	managed.times = make(map[string]*metav1.Time, len(encodedManagedFields))
 
 	for i, encodedVersionedSet := range encodedManagedFields {
+		switch encodedVersionedSet.Operation {
+		case metav1.ManagedFieldsOperationApply, metav1.ManagedFieldsOperationUpdate:
+		default:
+			return nil, fmt.Errorf("operation must be `Apply` or `Update`")
+		}
+		if len(encodedVersionedSet.APIVersion) < 1 {
+			return nil, fmt.Errorf("apiVersion must not be empty")
+		}
 		switch encodedVersionedSet.FieldsType {
 		case "FieldsV1":
 			// Valid case.
diff --git a/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/internal/managedfields_test.go b/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/internal/managedfields_test.go
index 1ca4d4b0ba0..f6df7228c13 100644
--- a/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/internal/managedfields_test.go
+++ b/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/internal/managedfields_test.go
@@ -72,6 +72,84 @@ func TestHasFieldsType(t *testing.T) {
 	}
 }
 
+// TestHasAPIVersion makes sure that we fail if we don't have an
+// APIVersion set.
+func TestHasAPIVersion(t *testing.T) {
+	var unmarshaled []metav1.ManagedFieldsEntry
+	if err := yaml.Unmarshal([]byte(`- apiVersion: v1
+  fieldsType: FieldsV1
+  fieldsV1:
+    f:field: {}
+  manager: foo
+  operation: Apply
+`), &unmarshaled); err != nil {
+		t.Fatalf("did not expect yaml unmarshalling error but got: %v", err)
+	}
+	if _, err := DecodeManagedFields(unmarshaled); err != nil {
+		t.Fatalf("did not expect decoding error but got: %v", err)
+	}
+
+	// Missing apiVersion.
+	unmarshaled = nil
+	if err := yaml.Unmarshal([]byte(`- fieldsType: FieldsV1
+  fieldsV1:
+    f:field: {}
+  manager: foo
+  operation: Apply
+`), &unmarshaled); err != nil {
+		t.Fatalf("did not expect yaml unmarshalling error but got: %v", err)
+	}
+	if _, err := DecodeManagedFields(unmarshaled); err == nil {
+		t.Fatal("Expect decoding error but got none")
+	}
+}
+
+// TestHasOperation makes sure that we fail if we don't have an
+// Operation set properly.
+func TestHasOperation(t *testing.T) {
+	var unmarshaled []metav1.ManagedFieldsEntry
+	if err := yaml.Unmarshal([]byte(`- apiVersion: v1
+  fieldsType: FieldsV1
+  fieldsV1:
+    f:field: {}
+  manager: foo
+  operation: Apply
+`), &unmarshaled); err != nil {
+		t.Fatalf("did not expect yaml unmarshalling error but got: %v", err)
+	}
+	if _, err := DecodeManagedFields(unmarshaled); err != nil {
+		t.Fatalf("did not expect decoding error but got: %v", err)
+	}
+
+	// Invalid operation.
+	if err := yaml.Unmarshal([]byte(`- apiVersion: v1
+  fieldsType: FieldsV1
+  fieldsV1:
+    f:field: {}
+  manager: foo
+  operation: Invalid
+`), &unmarshaled); err != nil {
+		t.Fatalf("did not expect yaml unmarshalling error but got: %v", err)
+	}
+	if _, err := DecodeManagedFields(unmarshaled); err == nil {
+		t.Fatal("Expect decoding error but got none")
+	}
+
+	// Missing operation.
+	unmarshaled = nil
+	if err := yaml.Unmarshal([]byte(`- apiVersion: v1
+  fieldsType: FieldsV1
+  fieldsV1:
+    f:field: {}
+  manager: foo
+`), &unmarshaled); err != nil {
+		t.Fatalf("did not expect yaml unmarshalling error but got: %v", err)
+	}
+	if _, err := DecodeManagedFields(unmarshaled); err == nil {
+		t.Fatal("Expect decoding error but got none")
+	}
+}
+
 // TestRoundTripManagedFields will roundtrip ManagedFields from the wire format
 // (api format) to the format used by sigs.k8s.io/structured-merge-diff and back
 func TestRoundTripManagedFields(t *testing.T) {