diff --git a/src/pygit2/repository.c b/src/pygit2/repository.c
index 5d0fc84..daa2c44 100644
--- a/src/pygit2/repository.c
+++ b/src/pygit2/repository.c
@@ -182,16 +182,16 @@ Repository_as_iter(Repository *self)
     err = git_repository_odb(&odb, self->repo);
     if (err < 0) {
         Error_set(err);
-        return -1;
+        return NULL;
     }
     err = git_odb_foreach(odb, Repository_build_as_iter, (void*)accum);
     if (err == GIT_EUSER) {
         git_odb_free(odb);
-        return -1;
+        return NULL;
     } else if (err < 0) {
         git_odb_free(odb);
         Error_set(err);
-        return -1;
+        return NULL;
     }
 
     git_odb_free(odb);