diff --git a/src/freebsd/up-util.c b/src/freebsd/up-util.c
index 53007ac..9da6f91 100644
--- a/src/freebsd/up-util.c
+++ b/src/freebsd/up-util.c
@@ -145,7 +145,7 @@ up_make_safe_string (const gchar *text)
 				ret[idx] = ret[i];
 			idx++;
 		} else {
-			g_debug ("invalid char '%c'", ret[i]);
+			g_debug ("invalid char 0x%02X", ret[i]);
 		}
 	}
 
diff --git a/src/linux/up-device-supply.c b/src/linux/up-device-supply.c
index 4936dbf..0cf5ac4 100644
--- a/src/linux/up-device-supply.c
+++ b/src/linux/up-device-supply.c
@@ -431,7 +431,7 @@ up_device_supply_make_safe_string (gchar *text)
 				text[idx] = text[i];
 			idx++;
 		} else {
-			g_debug ("invalid char '%c'", text[i]);
+			g_debug ("invalid char: 0x%02X", text[i]);
 		}
 	}