--- a/browser/components/enterprisepolicies/Policies.jsm
+++ b/browser/components/enterprisepolicies/Policies.jsm
@@ -691,17 +691,17 @@ var Policies = {
           // Only rerun if the list of engine names has changed.
           let engineNameList = param.Add.map(engine => engine.Name);
           runOncePerModification("addSearchEngines",
                                  JSON.stringify(engineNameList),
                                  () => {
             for (let newEngine of param.Add) {
               let newEngineParameters = {
                 template:    newEngine.URLTemplate,
-                iconURL:     newEngine.IconURL,
+                iconURL:     newEngine.IconURL.spec,
                 alias:       newEngine.Alias,
                 description: newEngine.Description,
                 method:      newEngine.Method,
                 suggestURL:  newEngine.SuggestURLTemplate,
                 extensionID: "set-via-policy"
               };
               try {
                 Services.search.addEngineWithDetails(newEngine.Name,