diff --git a/arch/x86_64/src/common/x86_64_allocateheap.c b/arch/x86_64/src/common/x86_64_allocateheap.c
index f75aa4c6494..ce23491f77b 100644
--- a/arch/x86_64/src/common/x86_64_allocateheap.c
+++ b/arch/x86_64/src/common/x86_64_allocateheap.c
@@ -55,8 +55,10 @@
  * Public Functions
  ****************************************************************************/
 
+/* The CPU0 idle stack starts at _ebss */
+
 const uintptr_t g_idle_topstack = (uintptr_t)_ebss +
-                                  CONFIG_IDLETHREAD_STACKSIZE - 16;
+                                  CONFIG_IDLETHREAD_STACKSIZE;
 
 /****************************************************************************
  * Name: up_allocate_heap