diff --git a/openbsc/src/libmsc/vty_interface_layer3.c b/openbsc/src/libmsc/vty_interface_layer3.c
index 1515aea..71fff93 100644
--- a/openbsc/src/libmsc/vty_interface_layer3.c
+++ b/openbsc/src/libmsc/vty_interface_layer3.c
@@ -547,7 +547,7 @@
 
 	if (strlen(name) > sizeof(subscr->name)-1) {
 		vty_out(vty,
-			"%% NAME is too long, max. %d characters are allowed%s",
+			"%% NAME is too long, max. %zu characters are allowed%s",
 			sizeof(subscr->name)-1, VTY_NEWLINE);
 		return CMD_WARNING;
 	}
@@ -580,7 +580,7 @@
 
 	if (strlen(ext) > sizeof(subscr->extension)-1) {
 		vty_out(vty,
-			"%% EXTENSION is too long, max. %d characters are allowed%s",
+			"%% EXTENSION is too long, max. %zu characters are allowed%s",
 			sizeof(subscr->extension)-1, VTY_NEWLINE);
 		return CMD_WARNING;
 	}