diff --git a/test/engine/api/geary-account-mock.vala b/test/engine/api/geary-account-mock.vala
index 2159df5a..9f72dedc 100644
--- a/test/engine/api/geary-account-mock.vala
+++ b/test/engine/api/geary-account-mock.vala
@@ -109,7 +109,7 @@ public class Geary.MockAccount : Account, MockObject {
     public override EmailIdentifier to_email_identifier(GLib.Variant serialised)
         throws EngineError.BAD_PARAMETERS {
         try {
-            return object_or_throw_call(
+            return object_or_throw_call<EmailIdentifier>(
                 "to_email_identifier",
                 { box_arg(serialised) },
                 new EngineError.BAD_PARAMETERS("Mock error")
@@ -124,7 +124,7 @@ public class Geary.MockAccount : Account, MockObject {
     public override FolderPath to_folder_path(GLib.Variant serialised)
         throws EngineError.BAD_PARAMETERS {
         try {
-            return object_or_throw_call(
+            return object_or_throw_call<FolderPath>(
                 "to_folder_path",
                 { box_arg(serialised) },
                 new EngineError.BAD_PARAMETERS("Mock error")
@@ -139,7 +139,7 @@ public class Geary.MockAccount : Account, MockObject {
     public override Folder get_folder(FolderPath path)
         throws EngineError.NOT_FOUND {
         try {
-            return object_or_throw_call(
+            return object_or_throw_call<Folder>(
                 "get_folder",
                 { path },
                 new EngineError.NOT_FOUND("Mock error")
diff --git a/test/engine/imap-db/imap-db-folder-test.vala b/test/engine/imap-db/imap-db-folder-test.vala
index 0e5c6693..496afd10 100644
--- a/test/engine/imap-db/imap-db-folder-test.vala
+++ b/test/engine/imap-db/imap-db-folder-test.vala
@@ -60,7 +60,7 @@ class Geary.ImapDB.FolderTest : TestCase {
             null,
             (obj, ret) => { async_complete(ret); }
         );
-        this.folder = traverse(
+        this.folder = traverse<Folder>(
             this.account.list_folders_async.end(async_result())
         ).first();
     }