diff --git a/moto/ec2/models.py b/moto/ec2/models.py
index 80bbf843..932f535a 100755
--- a/moto/ec2/models.py
+++ b/moto/ec2/models.py
@@ -48,6 +48,7 @@ from .exceptions import (
     InvalidRouteError,
     InvalidInstanceIdError,
     InvalidAMIIdError,
+    MalformedAMIIdError,
     InvalidAMIAttributeItemValueError,
     InvalidSnapshotIdError,
     InvalidVolumeIdError,
@@ -1122,6 +1123,9 @@ class Ami(TaggedEC2Resource):
 
 
 class AmiBackend(object):
+
+    AMI_REGEX = re.compile("ami-[a-z0-9]+")
+
     def __init__(self):
         self.amis = {}
 
@@ -1170,6 +1174,12 @@ class AmiBackend(object):
 
         if ami_ids:
             images = [ami for ami in images if ami.id in ami_ids]
+            if len(ami_ids) > len(images):
+                unknown_ids = set(ami_ids) - set(images)
+                for id in unknown_ids:
+                    if not self.AMI_REGEX.match(id):
+                        raise MalformedAMIIdError(id)
+                raise InvalidAMIIdError(unknown_ids)
 
         # Generic filters
         if filters:
diff --git a/tests/test_ec2/test_amis.py b/tests/test_ec2/test_amis.py
index 1029ba39..9ba78241 100755
--- a/tests/test_ec2/test_amis.py
+++ b/tests/test_ec2/test_amis.py
@@ -8,6 +8,7 @@ import boto3
 import boto.ec2
 import boto3
 from boto.exception import EC2ResponseError, EC2ResponseError
+from botocore.exceptions import ClientError
 
 import sure  # noqa
 
@@ -666,6 +667,19 @@ def test_ami_attribute_error_cases():
     cm.exception.request_id.should_not.be.none
 
 
+@mock_ec2
+def test_ami_describe_non_existent():
+    ec2 = boto3.resource('ec2', region_name='us-west-1')
+    # Valid pattern but non-existent id
+    img = ec2.Image('ami-abcd1234')
+    with assert_raises(ClientError):
+        img.load()
+    # Invalid ami pattern
+    img = ec2.Image('not_an_ami_id')
+    with assert_raises(ClientError):
+        img.load()
+
+
 @mock_ec2
 def test_ami_filter_wildcard():
     ec2 = boto3.resource('ec2', region_name='us-west-1')