diff --git a/src/gamedata/keysections.cpp b/src/gamedata/keysections.cpp
index 763d5331f..e96a3042b 100644
--- a/src/gamedata/keysections.cpp
+++ b/src/gamedata/keysections.cpp
@@ -175,7 +175,7 @@ void D_LoadWadSettings ()
 
 		while (conf < eof)
 		{
-			size_t linePos = 0;
+			ptrdiff_t linePos = 0;
 
 			// Fetch a line to execute
 			command.Clear();