diff --git a/doc/doxygen/main_page.h b/doc/doxygen/main_page.h
index 24a59876..79e4eca6 100644
--- a/doc/doxygen/main_page.h
+++ b/doc/doxygen/main_page.h
@@ -122,7 +122,7 @@
  * running on target system) or @ref lwip_os (there is an OS running
  * on the target system).
  * 
- * See also: @ref multithreading
+ * See also: @ref multithreading (especially the part about @ref LWIP_ASSERT_CORE_LOCKED()!)
  *
  * Mainloop Mode
  * -------------
diff --git a/src/include/lwip/opt.h b/src/include/lwip/opt.h
index 4fbdc03e..301a47c1 100644
--- a/src/include/lwip/opt.h
+++ b/src/include/lwip/opt.h
@@ -218,7 +218,7 @@
  * requirements are satisfied during current function call.
  * This macro usually calls a function that is implemented in the OS-dependent
  * sys layer and performs the following checks:
- * - Not in ISR
+ * - Not in ISR (this should be checked for NO_SYS==1, too!)
  * - If @ref LWIP_TCPIP_CORE_LOCKING = 1: TCPIP core lock is held
  * - If @ref LWIP_TCPIP_CORE_LOCKING = 0: function is called from TCPIP thread
  * @see @ref multithreading