Index: kernel/generic/src/printf/printf_core.c
===================================================================
--- kernel/generic/src/printf/printf_core.c	(revision 043eca01ebb6b34f0caa6ca86a4c3c3ccae6a121)
+++ kernel/generic/src/printf/printf_core.c	(revision f049eec2e8912b45680161e172155481212b2b38)
@@ -82,4 +82,5 @@
 static char digits_small[] = "0123456789abcdef";
 static char digits_big[] = "0123456789ABCDEF";
+static char invalch = U_SPECIAL;
 
 /** Print one or more characters without adding newline.