diff --git a/Common/File/DiskFree.h b/Common/File/DiskFree.h
index a5a5fb3c68..97cc8b652b 100644
--- a/Common/File/DiskFree.h
+++ b/Common/File/DiskFree.h
@@ -5,5 +5,6 @@
 #include "Common/File/Path.h"
 
 // If this fails, false is returned and space is negative.
-// Try to avoid calling this from the main thread, if possible. Can be SLOW.
+// Try to avoid calling this from the main thread, if possible. Not super fast,
+// but is also not allowed to do things like scan the entire disk.
 bool free_disk_space(const Path &path, int64_t &space);
diff --git a/Core/FileSystems/MetaFileSystem.cpp b/Core/FileSystems/MetaFileSystem.cpp
index 1ab0e2cb94..03e211392e 100644
--- a/Core/FileSystems/MetaFileSystem.cpp
+++ b/Core/FileSystems/MetaFileSystem.cpp
@@ -682,3 +682,9 @@ int64_t MetaFileSystem::ComputeRecursiveDirectorySize(const std::string &filenam
 		return false;
 	}
 }
+
+bool MetaFileSystem::ComputeRecursiveDirSizeIfFast(const std::string &path, int64_t *size) {
+	// Shouldn't be called. Can't recurse MetaFileSystem.
+	_dbg_assert_(false);
+	return false;
+}
diff --git a/Core/FileSystems/MetaFileSystem.h b/Core/FileSystems/MetaFileSystem.h
index 3736e91204..41390e8ac2 100644
--- a/Core/FileSystems/MetaFileSystem.h
+++ b/Core/FileSystems/MetaFileSystem.h
@@ -144,16 +144,7 @@ public:
 
 	int64_t ComputeRecursiveDirectorySize(const std::string &dirPath);
 
-	// Shouldn't ever be called, but meh.
-	bool ComputeRecursiveDirSizeIfFast(const std::string &path, int64_t *size) override {
-		int64_t sizeTemp = ComputeRecursiveDirectorySize(path);
-		if (sizeTemp >= 0) {
-			*size = sizeTemp;
-			return true;
-		} else {
-			return false;
-		}
-	}
+	bool ComputeRecursiveDirSizeIfFast(const std::string &path, int64_t *size) override;
 
 	void Describe(char *buf, size_t size) const override { snprintf(buf, size, "Meta"); }