diff --git a/source/common/utility/cmdlib.cpp b/source/common/utility/cmdlib.cpp
index c0fc1dcb0..dcae2ec8d 100644
--- a/source/common/utility/cmdlib.cpp
+++ b/source/common/utility/cmdlib.cpp
@@ -47,6 +47,7 @@
 #endif
 #endif
 #include "cmdlib.h"
+#include "compat.h"
 
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -757,3 +758,17 @@ bool IsAbsPath(const char *name)
 #endif /* _WIN32 */
     return 0;
 }
+
+//==========================================================================
+//
+//
+//
+//==========================================================================
+
+void NormalizeFileName(FString &str)
+{
+	auto strp = str.LockBuffer();
+	Bcorrectfilename(strp, false);
+	str.UnlockBuffer();
+}
+
diff --git a/source/common/utility/cmdlib.h b/source/common/utility/cmdlib.h
index 045037651..cda5b8a74 100644
--- a/source/common/utility/cmdlib.h
+++ b/source/common/utility/cmdlib.h
@@ -27,6 +27,7 @@ bool DirEntryExists (const char *pathname, bool *isdir = nullptr);
 extern	FString progdir;
 
 void 	DefaultExtension (FString &path, const char *extension);
+void NormalizeFileName(FString &str);
 
 FString	ExtractFilePath (const char *path);
 FString	ExtractFileBase (const char *path, bool keep_extension=false);
diff --git a/source/duke3d/src/game.cpp b/source/duke3d/src/game.cpp
index ca79bfbc1..759310fda 100644
--- a/source/duke3d/src/game.cpp
+++ b/source/duke3d/src/game.cpp
@@ -5656,38 +5656,30 @@ static void G_Startup(void)
 
     if (userConfig.CommandMap.IsNotEmpty())
     {
+		FString startupMap;
         if (VOLUMEONE)
         {
             initprintf("The -map option is available in the registered version only!\n");
-            boardfilename[0] = 0;
         }
         else
         {
-            char *dot, *slash;
+			startupMap = userConfig.CommandMap;
+			if (startupMap.IndexOfAny("/\\") < 0) startupMap.Insert(0, "/");
+			DefaultExtension(startupMap, ".map");
+			startupMap.Substitute("\\", "/");
+			NormalizeFileName(startupMap);
 
-            boardfilename[0] = '/';
-            boardfilename[1] = 0;
-            Bstrcat(boardfilename, userConfig.CommandMap);
-
-            dot = Bstrrchr(boardfilename,'.');
-            slash = Bstrrchr(boardfilename,'/');
-            if (!slash) slash = Bstrrchr(boardfilename,'\\');
-
-            if ((!slash && !dot) || (slash && dot < slash))
-                Bstrcat(boardfilename,".map");
-
-            Bcorrectfilename(boardfilename,0);
-
-			if (fileSystem.FileExists(boardfilename))
+			if (fileSystem.FileExists(startupMap))
 			{
-                initprintf("Using level: \"%s\".\n",boardfilename);
+                initprintf("Using level: \"%s\".\n",startupMap.GetChars());
             }
             else
             {
-                initprintf("Level \"%s\" not found.\n",boardfilename);
+                initprintf("Level \"%s\" not found.\n",startupMap.GetChars());
                 boardfilename[0] = 0;
             }
         }
+		strncpy(boardfilename, startupMap, BMAX_PATH);
     }
 
     for (i=0; i<MAXPLAYERS; i++)
diff --git a/source/rr/src/game.cpp b/source/rr/src/game.cpp
index cc9faa2c5..d7b1a3336 100644
--- a/source/rr/src/game.cpp
+++ b/source/rr/src/game.cpp
@@ -7094,38 +7094,30 @@ static void G_Startup(void)
 
 	if (userConfig.CommandMap.IsNotEmpty())
 	{
+		FString startupMap;
         if (VOLUMEONE)
         {
             initprintf("The -map option is available in the registered version only!\n");
-            boardfilename[0] = 0;
         }
         else
         {
-            char *dot, *slash;
+			startupMap = userConfig.CommandMap;
+			if (startupMap.IndexOfAny("/\\") < 0) startupMap.Insert(0, "/");
+			DefaultExtension(startupMap, ".map");
+			startupMap.Substitute("\\", "/");
+			NormalizeFileName(startupMap);
 
-            boardfilename[0] = '/';
-            boardfilename[1] = 0;
-            Bstrcat(boardfilename, userConfig.CommandMap);
-
-            dot = Bstrrchr(boardfilename,'.');
-            slash = Bstrrchr(boardfilename,'/');
-            if (!slash) slash = Bstrrchr(boardfilename,'\\');
-
-            if ((!slash && !dot) || (slash && dot < slash))
-                Bstrcat(boardfilename,".map");
-
-            Bcorrectfilename(boardfilename,0);
-
-            if (fileSystem.FileExists(boardfilename))
-            {
-                initprintf("Using level: \"%s\".\n",boardfilename);
+			if (fileSystem.FileExists(startupMap))
+			{
+                initprintf("Using level: \"%s\".\n",startupMap.GetChars());
             }
             else
             {
-                initprintf("Level \"%s\" not found.\n",boardfilename);
+                initprintf("Level \"%s\" not found.\n",startupMap.GetChars());
                 boardfilename[0] = 0;
             }
         }
+		strncpy(boardfilename, startupMap, BMAX_PATH);
     }
 
     for (i=0; i<MAXPLAYERS; i++)