diff --git a/src/p_setup.c b/src/p_setup.c
index c84b1ac78..d6cda7d4f 100644
--- a/src/p_setup.c
+++ b/src/p_setup.c
@@ -4218,7 +4218,8 @@ static void P_ConvertBinaryLinedefTypes(void)
 			lines[i].args[0] = sides[lines[i].sidenum[0]].textureoffset >> FRACBITS;
 			lines[i].args[1] = sides[lines[i].sidenum[0]].rowoffset >> FRACBITS;
 			lines[i].args[2] = !!(lines[i].flags & ML_SKEWTD);
-			P_WriteConstant(sides[lines[i].sidenum[0]].toptexture, &lines[i].stringargs[0]);
+			if (sides[lines[i].sidenum[0]].toptexture)
+				P_WriteConstant(sides[lines[i].sidenum[0]].toptexture, &lines[i].stringargs[0]);
 			break;
 		case 16: //Minecart parameters
 			lines[i].args[0] = sides[lines[i].sidenum[0]].textureoffset >> FRACBITS;