diff --git a/include/drives.h b/include/drives.h
index 5f5b9e16..6a4e3b3d 100644
--- a/include/drives.h
+++ b/include/drives.h
@@ -22,7 +22,7 @@
 #include "dosbox.h"
 
 #include <memory>
-#include <set>
+#include <unordered_set>
 #include <string>
 #include <vector>
 
@@ -83,8 +83,8 @@ protected:
 	} srchInfo[MAX_OPENDIRS];
 
 private:
-	virtual bool IsFirstEncounter(const std::string& filename);
-	std::set<std::string> write_protected_files;
+	bool IsFirstEncounter(const std::string& filename);
+	std::unordered_set<std::string> write_protected_files;
 	struct {
 		Bit16u bytes_sector;
 		Bit8u sectors_cluster;
diff --git a/src/dos/drive_local.cpp b/src/dos/drive_local.cpp
index e49be66a..21a622a9 100644
--- a/src/dos/drive_local.cpp
+++ b/src/dos/drive_local.cpp
@@ -65,9 +65,9 @@ bool localDrive::FileCreate(DOS_File * * file,char * name,Bit16u /*attributes*/)
 }
 
 bool localDrive::IsFirstEncounter(const std::string& filename) {
-	const std::pair<std::set<std::string>::iterator, bool> \
-		ret(write_protected_files.insert(filename));
-	return ret.second;
+	const auto ret = write_protected_files.insert(filename);
+	const bool was_inserted = ret.second;
+	return was_inserted;
 }
 
 bool localDrive::FileOpen(DOS_File** file, char * name, Bit32u flags) {