diff --git a/CryptoPkg/Library/BaseCryptLibMbedTls/SysCall/ConstantTimeClock.c b/CryptoPkg/Library/BaseCryptLibMbedTls/SysCall/ConstantTimeClock.c
index e6e0f1ec2df0..6fba009588c4 100644
--- a/CryptoPkg/Library/BaseCryptLibMbedTls/SysCall/ConstantTimeClock.c
+++ b/CryptoPkg/Library/BaseCryptLibMbedTls/SysCall/ConstantTimeClock.c
@@ -47,6 +47,15 @@ gmtime (
   return NULL;
 }
 
+/**sleep function. **/
+unsigned int
+sleep(
+  unsigned int  seconds
+)
+{
+  return 0;
+}
+
 /**_time64 function. **/
 time_t
 _time64 (