Index: sys/amd64/include/counter.h
===================================================================
--- sys/amd64/include/counter.h
+++ sys/amd64/include/counter.h
@@ -82,6 +82,7 @@
 counter_u64_add(counter_u64_t c, int64_t inc)
 {
 
+	KASSERT(IS_BSP() || c != EARLY_COUNTER, ("EARLY_COUNTER used on AP"));
 	__asm __volatile("addq\t%1,%%gs:(%0)"
 	    :
 	    : "r" ((char *)c - (char *)&__pcpu[0]), "ri" (inc)