diff --git a/src/knownnetworks.c b/src/knownnetworks.c
index 6c575e50..d4d50a6f 100644
--- a/src/knownnetworks.c
+++ b/src/knownnetworks.c
@@ -174,7 +174,7 @@ static const char *known_network_get_path(const struct network_info *network)
 
 	for (i = 0; network->ssid[i] && pos < sizeof(path); i++)
 		pos += snprintf(path + pos, sizeof(path) - pos, "%02x",
-				network->ssid[i]);
+				(unsigned char)network->ssid[i]);
 
 	if (pos < sizeof(path))
 		snprintf(path + pos, sizeof(path) - pos, "_%s",