diff --git a/src/include/lwip/arch.h b/src/include/lwip/arch.h
index eacab667..524af6be 100644
--- a/src/include/lwip/arch.h
+++ b/src/include/lwip/arch.h
@@ -46,6 +46,11 @@
 #ifndef SZT_F
 #define SZT_F U32_F
 #endif /* SZT_F */
+/** Temporary upgrade helper: define format string for u8_t as hex if not
+    defined in cc.h */
+#ifndef X8_F
+#define X8_F  "02x"
+#endif /* X8_F */
 
 #ifdef __cplusplus
 extern "C" {