diff --git a/packages/shared/sdk-server/__tests__/MigrationOpTracker.test.ts b/packages/shared/sdk-server/__tests__/MigrationOpTracker.test.ts
index 8346aa2b5..4c44f80bf 100644
--- a/packages/shared/sdk-server/__tests__/MigrationOpTracker.test.ts
+++ b/packages/shared/sdk-server/__tests__/MigrationOpTracker.test.ts
@@ -14,6 +14,8 @@ it('does not generate an event if an op is not set', () => {
     },
   );
 
+  tracker.invoked('old');
+
   expect(tracker.createEvent()).toBeUndefined();
 });
 
@@ -22,8 +24,27 @@ it('does not generate an event with missing context keys', () => {
     kind: 'FALLTHROUGH',
   });
 
-  // Set the op otherwise that would prevent an event as well.
+  // Set the op otherwise/invoked that would prevent an event as well.
   tracker.op('write');
+  tracker.invoked('old');
+
+  expect(tracker.createEvent()).toBeUndefined();
+});
+
+it('does not generate an event with empty flag key', () => {
+  const tracker = new MigrationOpTracker(
+    '',
+    { key: 'user-key' },
+    LDMigrationStage.Off,
+    LDMigrationStage.Off,
+    {
+      kind: 'FALLTHROUGH',
+    },
+  );
+
+  // Set the op/invoked otherwise that would prevent an event as well.
+  tracker.op('write');
+  tracker.invoked('old');
 
   expect(tracker.createEvent()).toBeUndefined();
 });
diff --git a/packages/shared/sdk-server/src/MigrationOpTracker.ts b/packages/shared/sdk-server/src/MigrationOpTracker.ts
index 9001e42fd..fae4884bf 100644
--- a/packages/shared/sdk-server/src/MigrationOpTracker.ts
+++ b/packages/shared/sdk-server/src/MigrationOpTracker.ts
@@ -1,4 +1,9 @@
-import { internal, LDEvaluationReason, LDLogger } from '@launchdarkly/js-sdk-common';
+import {
+  internal,
+  LDEvaluationReason,
+  LDLogger,
+  TypeValidators,
+} from '@launchdarkly/js-sdk-common';
 
 import { LDMigrationStage, LDMigrationTracker } from './api';
 import {
@@ -82,6 +87,11 @@ export default class MigrationOpTracker implements LDMigrationTracker {
   }
 
   createEvent(): LDMigrationOpEvent | undefined {
+    if (!TypeValidators.String.is(this.flagKey) || this.flagKey === '') {
+      this.logger?.error('The flag key for a migration operation must be a non-empty string.');
+      return undefined;
+    }
+
     if (!this.operation) {
       this.logger?.error('The operation must be set using "op" before an event can be created.');
       return undefined;