diff --git a/src/mwindow.c b/src/mwindow.c
index a03a6597e..1d64d26a4 100644
--- a/src/mwindow.c
+++ b/src/mwindow.c
@@ -62,8 +62,10 @@ int git_mwindow_get_pack(struct git_pack_file **out, const char *path)
 	if ((error = git_packfile__name(&packname, path)) < 0)
 		return error;
 
-	if (git_mutex_lock(&git__mwindow_mutex) < 0)
+	if (git_mutex_lock(&git__mwindow_mutex) < 0) {
+		giterr_set(GITERR_OS, "failed to lock mwindow mutex");
 		return -1;
+	}
 
 	if (git_mwindow_files_init() < 0) {
 		git_mutex_unlock(&git__mwindow_mutex);
@@ -103,24 +105,20 @@ int git_mwindow_get_pack(struct git_pack_file **out, const char *path)
 	return 0;
 }
 
-int git_mwindow_put_pack(struct git_pack_file *pack)
+void git_mwindow_put_pack(struct git_pack_file *pack)
 {
 	int count;
 	git_strmap_iter pos;
 
 	if (git_mutex_lock(&git__mwindow_mutex) < 0)
-		return -1;
+		return;
 
-	if (git_mwindow_files_init() < 0) {
-		git_mutex_unlock(&git__mwindow_mutex);
-		return -1;
-	}
+	/* put before get would be a corrupted state */
+	assert(git__pack_cache);
 
 	pos = git_strmap_lookup_index(git__pack_cache, pack->pack_name);
-	if (!git_strmap_valid_index(git__pack_cache, pos)) {
-		git_mutex_unlock(&git__mwindow_mutex);
-		return GIT_ENOTFOUND;
-	}
+	/* if we cannot find it, the state is corrupted */
+	assert(git_strmap_valid_index(git__pack_cache, pos));
 
 	count = git_atomic_dec(&pack->refcount);
 	if (count == 0) {
@@ -129,7 +127,7 @@ int git_mwindow_put_pack(struct git_pack_file *pack)
 	}
 
 	git_mutex_unlock(&git__mwindow_mutex);
-	return 0;
+	return;
 }
 
 void git_mwindow_free_all(git_mwindow_file *mwf)
diff --git a/src/mwindow.h b/src/mwindow.h
index 57fabae70..63418e458 100644
--- a/src/mwindow.h
+++ b/src/mwindow.h
@@ -48,6 +48,6 @@ void git_mwindow_files_free(void);
 
 struct git_pack_file; /* just declaration to avoid cyclical includes */
 int git_mwindow_get_pack(struct git_pack_file **out, const char *path);
-int git_mwindow_put_pack(struct git_pack_file *pack);
+void git_mwindow_put_pack(struct git_pack_file *pack);
 
 #endif