diff --git a/toolkit/components/extensions/test/xpcshell/test_locale_converter.js b/toolkit/components/extensions/test/xpcshell/test_locale_converter.js
index e296a66127ba..c8b1ee92bab7 100644
--- a/toolkit/components/extensions/test/xpcshell/test_locale_converter.js
+++ b/toolkit/components/extensions/test/xpcshell/test_locale_converter.js
@@ -123,3 +123,11 @@ add_task(function* testInvalidUUID() {
     convService.asyncConvertData(FROM_TYPE, TO_TYPE, listener, uri);
   }, expectInvalidContextException);
 });
+
+
+// Test that an empty stream does not throw an NS_ERROR_ILLEGAL_VALUE.
+add_task(function* testEmptyStream() {
+  let stream = StringStream("");
+  let resultStream = convService.convert(stream, FROM_TYPE, TO_TYPE, URI);
+  equal(resultStream.data, "");
+});
diff --git a/toolkit/components/utils/simpleServices.js b/toolkit/components/utils/simpleServices.js
index a3befe188938..b58c4d4962c1 100644
--- a/toolkit/components/utils/simpleServices.js
+++ b/toolkit/components/utils/simpleServices.js
@@ -225,7 +225,10 @@ AddonLocalizationConverter.prototype = {
     this.checkTypes(aFromType, aToType);
     let addonId = this.getAddonId(aContext);
 
-    let string = NetUtil.readInputStreamToString(aStream, aStream.available());
+    let string = (
+      aStream.available() ?
+      NetUtil.readInputStreamToString(aStream, aStream.available()): ""
+    );
     return this.convertToStream(addonId, string);
   },