diff --git a/moto/ec2/models.py b/moto/ec2/models.py
index f86b1852c..5599802f6 100644
--- a/moto/ec2/models.py
+++ b/moto/ec2/models.py
@@ -1240,7 +1240,6 @@ class SecurityGroupBackend(object):
     def get_security_group_from_id(self, group_id):
         # 2 levels of chaining necessary since it's a complex structure
         all_groups = itertools.chain.from_iterable([x.values() for x in self.groups.values()])
-
         for group in all_groups:
             if group.id == group_id:
                 return group
@@ -1267,7 +1266,6 @@ class SecurityGroupBackend(object):
                                          source_group_ids=None,
                                          vpc_id=None):
         group = self.get_security_group_by_name_or_id(group_name_or_id, vpc_id)
-
         if ip_ranges and not isinstance(ip_ranges, list):
             ip_ranges = [ip_ranges]
         if ip_ranges:
@@ -1335,8 +1333,10 @@ class SecurityGroupBackend(object):
 
         group = self.get_security_group_by_name_or_id(group_name_or_id, vpc_id)
 
-        if ip_ranges and not isinstance(ip_ranges, list):
-            ip_ranges = [ip_ranges]
+        if ip_ranges:
+            for cidr in ip_ranges:
+                if not is_valid_cidr(cidr):
+                    raise InvalidCIDRSubnetError(cidr=cidr)
 
         # for VPCs
         source_groups = []