diff --git a/src/index.js b/src/index.js
index 28d077a..f46986e 100644
--- a/src/index.js
+++ b/src/index.js
@@ -237,7 +237,12 @@ class AlertsPlugin {
 
     if (topic) {
       if (isTopicConfigAnImport || topic.indexOf('arn:') === 0) {
-        alertTopics[key] = topic;
+        if (customAlarmName) {
+          alertTopics[customAlarmName] = alertTopics[customAlarmName] || {};
+          alertTopics[customAlarmName][key] = topic;
+        } else {
+          alertTopics[key] = topic;
+        }
       } else {
         const cfRef = `AwsAlerts${customAlarmName ? _.upperFirst(customAlarmName) : ''}${_.upperFirst(key)}`;
         if (customAlarmName) {
diff --git a/src/index.test.js b/src/index.test.js
index 62b7c3d..d2c2748 100644
--- a/src/index.test.js
+++ b/src/index.test.js
@@ -411,6 +411,38 @@ describe('#index', function () {
       expect(plugin.serverless.service.provider.compiledCloudFormationTemplate.Resources).toEqual({});
     });
 
+    it('should not create SNS topic when ARN is passed to custom topic', () => {
+      const topicName = 'arn:aws:sns:us-east-1:123456789012:ok-topic';
+
+      const plugin = pluginFactory({
+        topics: {
+          customAlert: {
+            alarm: {
+              topic: topicName,
+            },
+            ok: {
+              topic: topicName,
+            },
+          },
+        },
+      });
+
+      const config = plugin.getConfig();
+      const topics = plugin.compileAlertTopics(config);
+
+      expect(topics).toEqual({
+        customAlert: {
+          alarm: topicName,
+          ok: topicName,
+        },
+      });
+
+      expect(
+        plugin.serverless.service.provider.compiledCloudFormationTemplate
+          .Resources
+      ).toEqual({});
+    });
+
     it('should create SNS topic when name is passed', () => {
       const topicName = 'ok-topic';
       const plugin = pluginFactory({