diff --git a/sources/test-Z80.c b/sources/test-Z80.c
index 87ec46b..70dedd8 100644
--- a/sources/test-Z80.c
+++ b/sources/test-Z80.c
@@ -662,8 +662,8 @@ int main(int argc, char **argv)
 				"\n"
 				"Options:\n"
 				"  -V, --verbosity (0..4)  Set the verbosity level (the default level is 4).\n"
-				"  -0, --in-even <value>   Set the 8-bit value to be read from even I/O ports.\n"
-				"  -1, --in-odd <value>    Set the 8-bit value to be read from odd I/O ports.\n"
+				"  -0, --in-even <0..255>  Set the 8-bit value to be read from even I/O ports.\n"
+				"  -1, --in-odd <0..255>   Set the 8-bit value to be read from odd I/O ports.\n"
 				"  -a, --all               Run all tests.\n"
 				"  -h, --help              Show this help message.\n"
 				"  -m, --model <model>     Specify the CPU model to emulate.\n"