diff --git a/moto/ec2/utils.py b/moto/ec2/utils.py
index ab54ea3a8..32122c763 100644
--- a/moto/ec2/utils.py
+++ b/moto/ec2/utils.py
@@ -51,7 +51,7 @@ def random_ami_id():
 
 
 def random_instance_id():
-    return random_id(prefix=EC2_RESOURCE_TO_PREFIX['instance'])
+    return random_id(prefix=EC2_RESOURCE_TO_PREFIX['instance'], size=17)
 
 
 def random_reservation_id():