diff --git a/src/include/lwip/def.h b/src/include/lwip/def.h
index 95d2d70c..35359b3a 100644
--- a/src/include/lwip/def.h
+++ b/src/include/lwip/def.h
@@ -138,16 +138,21 @@ u32_t lwip_ntohl(u32_t x);
  * your platform to save some code bytes if you use these functions
  * in your application, too.
  */
+
 #ifndef lwip_itoa
+/* This can be #defined to itoa() or snprintf(result, bufsize, "%d", number) depending on your platform */
 void  lwip_itoa(char* result, size_t bufsize, int number);
 #endif
 #ifndef lwip_strnicmp
+/* This can be #defined to strnicmp() or strncasecmp() depending on your platform */
 int   lwip_strnicmp(const char* str1, const char* str2, size_t len);
 #endif
 #ifndef lwip_stricmp
+/* This can be #defined to stricmp() or strcasecmp() depending on your platform */
 int   lwip_stricmp(const char* str1, const char* str2);
 #endif
 #ifndef lwip_strnstr
+/* This can be #defined to strnstr() depending on your platform */
 char* lwip_strnstr(const char* buffer, const char* token, size_t n);
 #endif