diff --git a/seminaries/qtmips/print-hex-to-uart/Makefile b/seminaries/qtmips/print-hex-to-uart/Makefile
index 42e2f58b6c1947be68fa89a0cc941af668ebcff3..5cf6cd7d6cc02c7a7f359b76c79422a863e002d9 100644
--- a/seminaries/qtmips/print-hex-to-uart/Makefile
+++ b/seminaries/qtmips/print-hex-to-uart/Makefile
@@ -83,7 +83,8 @@ run_test: $(TARGET_EXE)
 	printf "%08x\n" $(input_val) >serial_port.ref
 	qtmips_cli --pipelined \
 		--dump-cycles $< \
-		--load-range input_val,input_val.in
+		--load-range input_val,input_val.in \
+		--serout serial_port.out
 	diff -u serial_port.ref serial_port.out
 
 -include depend