diff --git a/x-pack/plugins/actions/server/builtin_action_types/slack.ts b/x-pack/plugins/actions/server/builtin_action_types/slack.ts
index 042853796695d6..3a351853c1e462 100644
--- a/x-pack/plugins/actions/server/builtin_action_types/slack.ts
+++ b/x-pack/plugins/actions/server/builtin_action_types/slack.ts
@@ -35,7 +35,7 @@ const SecretsSchema = schema.object(secretsSchemaProps);
 export type ActionParamsType = TypeOf<typeof ParamsSchema>;
 
 const ParamsSchema = schema.object({
-  message: schema.string(),
+  message: schema.string({ minLength: 1 }),
 });
 
 // action type definition
diff --git a/x-pack/test/alerting_api_integration/security_and_spaces/tests/actions/builtin_action_types/slack.ts b/x-pack/test/alerting_api_integration/security_and_spaces/tests/actions/builtin_action_types/slack.ts
index 5dcff8712a28d6..8afa43bfea21e6 100644
--- a/x-pack/test/alerting_api_integration/security_and_spaces/tests/actions/builtin_action_types/slack.ts
+++ b/x-pack/test/alerting_api_integration/security_and_spaces/tests/actions/builtin_action_types/slack.ts
@@ -159,6 +159,20 @@ export default function slackTest({ getService }: FtrProviderContext) {
       expect(result.status).to.eql('ok');
     });
 
+    it('should handle an empty message error', async () => {
+      const { body: result } = await supertest
+        .post(`/api/action/${simulatedActionId}/_execute`)
+        .set('kbn-xsrf', 'foo')
+        .send({
+          params: {
+            message: '',
+          },
+        })
+        .expect(200);
+      expect(result.status).to.eql('error');
+      expect(result.message).to.match(/error validating action params: \[message\]: /);
+    });
+
     it('should handle a 40x slack error', async () => {
       const { body: result } = await supertest
         .post(`/api/action/${simulatedActionId}/_execute`)