diff --git a/miosix/kernel/kernel.cpp b/miosix/kernel/kernel.cpp
index 80856516090149bbb492c4f04568ff50720a60e2..a07496be07c5e08ddda20f11c14d206c5611646e 100644
--- a/miosix/kernel/kernel.cpp
+++ b/miosix/kernel/kernel.cpp
@@ -63,7 +63,7 @@ volatile Thread *cur=NULL;///<\internal Thread currently running
 ///\internal True if there are threads in the DELETED status. Used by idle thread
 static volatile bool exist_deleted=false;
 
-SleepData *sleeping_list=NULL;///list of sleeping threads
+static SleepData *sleeping_list=NULL;///list of sleeping threads
 
 #ifndef USE_CSTIMER
 static volatile long long tick=0;///<\internal Kernel tick