diff --git a/lib/errors.js b/lib/errors.js
index 6aa605e..f2a04c2 100644
--- a/lib/errors.js
+++ b/lib/errors.js
@@ -21,7 +21,8 @@ const Reason = Object.freeze({
     RenditionFormatUnsupported: "RenditionFormatUnsupported",
     SourceUnsupported: "SourceUnsupported",
     SourceCorrupt: "SourceCorrupt",
-    RenditionTooLarge: "RenditionTooLarge"
+    RenditionTooLarge: "RenditionTooLarge",
+    ServiceOverLoad: "ServiceOverLoad"
 });
 
 
@@ -121,6 +122,14 @@ class RenditionTooLarge extends ClientError {
     }
 }
 
+// Worker encountered upstream API rate limiting. Client may resubmit request after some time.
+class ServiceOverLoadError extends ClientError {
+    constructor(message) {
+        super(message, "ServiceOverLoadError", Reason.ServiceOverLoad);
+
+        Error.captureStackTrace(this, ServiceOverLoadError);
+    }
+}
 
 module.exports = {
     GenericError,
@@ -131,5 +140,6 @@ module.exports = {
     SourceUnsupportedError,
     SourceCorruptError,
     RenditionTooLarge,
-    ArgumentError
+    ArgumentError,
+    ServiceOverLoadError
 };
diff --git a/test/errors.test.js b/test/errors.test.js
index 0443a55..3e99ec0 100644
--- a/test/errors.test.js
+++ b/test/errors.test.js
@@ -21,7 +21,8 @@ const {
     SourceFormatUnsupportedError,
     SourceUnsupportedError,
     SourceCorruptError,
-    RenditionTooLarge
+    RenditionTooLarge,
+    ServiceOverLoadError
 } = require('../lib/errors');
 
 describe("errors", function() {
@@ -98,4 +99,16 @@ describe("errors", function() {
             assert.equal(e.reason, Reason.RenditionTooLarge);
         }
     });
+
+    it("ServiceOverLoadError", function() {
+        try {
+            throw new ServiceOverLoadError("too many requests");
+        } catch (e) {
+            assert.ok(e instanceof ClientError);
+            assert.ok(e instanceof ServiceOverLoadError);
+            assert.equal(e.name, "ServiceOverLoadError");
+            assert.equal(e.message, "too many requests");
+            assert.equal(e.reason, Reason.ServiceOverLoad);
+        }
+    });
 });