diff --git a/arch/x86_64/include/intel64/irq.h b/arch/x86_64/include/intel64/irq.h
index 90e9372a91..3979c907dc 100644
--- a/arch/x86_64/include/intel64/irq.h
+++ b/arch/x86_64/include/intel64/irq.h
@@ -535,7 +535,7 @@ static inline uint64_t rdtscp(void)
   uint32_t lo;
   uint32_t hi;
 
-  asm volatile("rdtscp" : "=a" (lo), "=d" (hi)::"memory");
+  asm volatile("rdtscp" : "=a" (lo), "=d" (hi)::"ecx", "memory");
   return (uint64_t)lo | (((uint64_t)hi) << 32);
 }