diff --git a/src/fileops.c b/src/fileops.c
index ea9935ab1..0633f9b21 100644
--- a/src/fileops.c
+++ b/src/fileops.c
@@ -74,8 +74,13 @@ int gitfo_isdir(const char *path)
 		stat_error = gitfo_stat(path, &st);
 	}
 
-	return (stat_error == 0 && S_ISDIR(st.st_mode)) ? 
-		GIT_SUCCESS : GIT_ENOTFOUND;
+	if (stat_error < GIT_SUCCESS)
+		return GIT_ENOTFOUND;
+
+	if (!S_ISDIR(st.st_mode))
+		return GIT_ENOTFOUND;
+
+	return GIT_SUCCESS;
 }
 
 int gitfo_exists(const char *path)
diff --git a/src/odb.c b/src/odb.c
index 9dbe1ccd8..d54ad83fe 100644
--- a/src/odb.c
+++ b/src/odb.c
@@ -210,7 +210,8 @@ void git_odb_close(git_odb *db)
 {
 	unsigned int i;
 
-	assert(db);
+	if (db == NULL)
+		return;
 
 	for (i = 0; i < db->backends.length; ++i) {
 		git_odb_backend *b = git_vector_get(&db->backends, i);
diff --git a/src/repository.c b/src/repository.c
index f27f77cb3..098d09858 100644
--- a/src/repository.c
+++ b/src/repository.c
@@ -103,7 +103,6 @@ static int assign_repository_folders(git_repository *repo,
 	if (git_dir == NULL || gitfo_isdir(git_dir) < GIT_SUCCESS)
 		return GIT_ENOTFOUND;
 
-
 	/* store GIT_DIR */
 	path_len = strlen(git_dir);
 	strcpy(path_aux, git_dir);
@@ -279,6 +278,7 @@ int git_repository_open(git_repository **repo_out, const char *path)
 	if (error < GIT_SUCCESS)
 		goto cleanup;
 
+
 	error = git_odb_open(&repo->db, repo->path_odb);
 	if (error < GIT_SUCCESS)
 		goto cleanup;
@@ -296,7 +296,8 @@ void git_repository_free(git_repository *repo)
 	git_hashtable_iterator it;
 	git_object *object;
 
-	assert(repo);
+	if (repo == NULL)
+		return;
 
 	free(repo->path_workdir);
 	free(repo->path_index);
@@ -310,8 +311,13 @@ void git_repository_free(git_repository *repo)
 		git_object_free(object);
 
 	git_hashtable_free(repo->objects);
-	git_odb_close(repo->db);
-	git_index_free(repo->index);
+
+	if (repo->db != NULL)
+		git_odb_close(repo->db);
+
+	if (repo->index != NULL)
+		git_index_free(repo->index);
+
 	free(repo);
 }
 
@@ -511,7 +517,8 @@ int git_object_write(git_object *object)
 
 void git_object_free(git_object *object)
 {
-	assert(object);
+	if (object == NULL)
+		return;
 
 	git_object__source_close(object);
 	git_hashtable_remove(object->repo->objects, &object->id);
diff --git a/src/revwalk.c b/src/revwalk.c
index b724f77c8..f2eaa710f 100644
--- a/src/revwalk.c
+++ b/src/revwalk.c
@@ -77,6 +77,9 @@ int git_revwalk_new(git_revwalk **revwalk_out, git_repository *repo)
 
 void git_revwalk_free(git_revwalk *walk)
 {
+	if (walk == NULL)
+		return;
+
 	git_revwalk_reset(walk);
 	git_hashtable_free(walk->commits);
 	free(walk);
@@ -90,6 +93,8 @@ git_repository *git_revwalk_repository(git_revwalk *walk)
 
 int git_revwalk_sorting(git_revwalk *walk, unsigned int sort_mode)
 {
+	assert(walk);
+
 	if (walk->walking)
 		return GIT_EBUSY;
 
@@ -165,6 +170,7 @@ static git_revwalk_commit *insert_commit(git_revwalk *walk, git_commit *commit_o
 
 int git_revwalk_push(git_revwalk *walk, git_commit *commit)
 {
+	assert(walk && commit);
 	return insert_commit(walk, commit) ? GIT_SUCCESS : GIT_ENOMEM;
 }
 
@@ -186,6 +192,8 @@ static void mark_uninteresting(git_revwalk_commit *commit)
 int git_revwalk_hide(git_revwalk *walk, git_commit *commit)
 {
 	git_revwalk_commit *hide;
+
+	assert(walk && commit);
 	
 	hide = insert_commit(walk, commit);
 	if (hide == NULL)
@@ -216,6 +224,8 @@ git_commit *git_revwalk_next(git_revwalk *walk)
 {
 	git_revwalk_commit *next;
 
+	assert(walk);
+
 	if (!walk->walking)
 		prepare_walk(walk);
 
@@ -234,6 +244,8 @@ void git_revwalk_reset(git_revwalk *walk)
 	git_hashtable_iterator it;
 	git_revwalk_commit *commit;
 
+	assert(walk);
+
 	git_hashtable_iterator_init(walk->commits, &it);
 
 	while ((commit = (git_revwalk_commit *)