diff --git a/Core/FileSystems/MetaFileSystem.cpp b/Core/FileSystems/MetaFileSystem.cpp
index 8fba8dff00..adc86c0ebb 100644
--- a/Core/FileSystems/MetaFileSystem.cpp
+++ b/Core/FileSystems/MetaFileSystem.cpp
@@ -292,12 +292,14 @@ void MetaFileSystem::Mount(const std::string &prefix, std::shared_ptr<IFileSyste
 	fileSystems.push_back(x);
 }
 
+// Assumes the lock is held
 void MetaFileSystem::UnmountAll() {
 	fileSystems.clear();
 	currentDir.clear();
 }
 
 void MetaFileSystem::Unmount(const std::string &prefix) {
+	std::lock_guard<std::recursive_mutex> guard(lock);
 	for (auto iter = fileSystems.begin(); iter != fileSystems.end(); iter++) {
 		if (iter->prefix == prefix) {
 			fileSystems.erase(iter);
@@ -325,6 +327,7 @@ IFileSystem *MetaFileSystem::GetSystemFromFilename(const std::string &filename)
 }
 
 IFileSystem *MetaFileSystem::GetSystem(const std::string &prefix) {
+	std::lock_guard<std::recursive_mutex> guard(lock);
 	for (auto it = fileSystems.begin(); it != fileSystems.end(); ++it) {
 		if (it->prefix == NormalizePrefix(prefix))
 			return it->system.get();
diff --git a/Core/FileSystems/MetaFileSystem.h b/Core/FileSystems/MetaFileSystem.h
index a735106f68..0a2255566f 100644
--- a/Core/FileSystems/MetaFileSystem.h
+++ b/Core/FileSystems/MetaFileSystem.h
@@ -43,8 +43,9 @@ private:
 	currentDir_t currentDir;
 
 	std::string startingDirectory;
-	std::recursive_mutex lock;  // must be recursive
+	std::recursive_mutex lock;  // must be recursive. TODO: fix that
 
+	// Assumes the lock is held
 	void Reset() {
 		// This used to be 6, probably an attempt to replicate PSP handles.
 		// However, that's an artifact of using psplink anyway...