diff --git a/src/strutil.c b/src/strutil.c
index 52103622..bd22e368 100644
--- a/src/strutil.c
+++ b/src/strutil.c
@@ -1176,7 +1176,7 @@ const char *str_cchex(const void *buf, size_t len, int add_space) {
   int wd = 2 + !!add_space;
   char *ret = avr_cc_buffer(wd*len + 1);
   for(size_t i=0; i<len; i++)
-    sprintf(ret + i*wd, "%s%02X", " "+(3-wd), ((unsigned char *) buf)[i]);
+    sprintf(ret + i*wd, "%s%02X", &" "[3-wd], ((unsigned char *) buf)[i]);
   return ret;
 }