diff --git a/src/newgrf.cpp b/src/newgrf.cpp
index a015fe5ade..c0f59b92e2 100644
--- a/src/newgrf.cpp
+++ b/src/newgrf.cpp
@@ -6954,7 +6954,7 @@ static void GRFSound(ByteReader *buf)
 		if (type != 0xFF) {
 			grfmsg(1, "GRFSound: Unexpected RealSprite found, skipping");
 			FioSkipBytes(7);
-			SkipSpriteData(type, num - 8);
+			SkipSpriteData(type, len - 8);
 			continue;
 		}