diff --git a/src/gba/gba-bios.c b/src/gba/gba-bios.c
index 5227123a4..6e5ddb238 100644
--- a/src/gba/gba-bios.c
+++ b/src/gba/gba-bios.c
@@ -485,6 +485,6 @@ static void _unFilter(struct GBA* gba, uint32_t source, uint32_t dest, int inwid
 			dest += outwidth;
 		}
 		source += inwidth;
-		--remaining;
+		remaining -= outwidth;
 	}
 }