diff --git a/moto/ec2/responses/instances.py b/moto/ec2/responses/instances.py
index 532d703c9..1550fddeb 100644
--- a/moto/ec2/responses/instances.py
+++ b/moto/ec2/responses/instances.py
@@ -30,7 +30,7 @@ class InstanceResponse(BaseResponse):
         if max_results and len(reservations) > (start + max_results):
             next_token = reservations_resp[-1].id
         template = self.response_template(EC2_DESCRIBE_INSTANCES)
-        return template.render(reservations=reservations_resp, next_token=next_token)
+        return template.render(reservations=reservations_resp, next_token=next_token).replace('True', 'true').replace('False', 'false')
 
     def run_instances(self):
         min_count = int(self._get_param('MinCount', if_none='1'))
@@ -144,7 +144,12 @@ class InstanceResponse(BaseResponse):
         """
         Handles requests which are generated by code similar to:
 
-            instance.modify_attribute('blockDeviceMapping', {'/dev/sda1': True})
+            instance.modify_attribute(
+                BlockDeviceMappings=[{
+                    'DeviceName': '/dev/sda1',
+                    'Ebs': {'DeleteOnTermination': True}
+                }]
+            )
 
         The querystring contains information similar to:
 
diff --git a/tests/test_ec2/test_instances.py b/tests/test_ec2/test_instances.py
index 04e6a6daa..46bb34d57 100644
--- a/tests/test_ec2/test_instances.py
+++ b/tests/test_ec2/test_instances.py
@@ -1113,3 +1113,20 @@ def test_get_instance_by_security_group():
 
     assert len(security_group_instances) == 1
     assert security_group_instances[0].id == instance.id
+
+
+@mock_ec2
+def test_modify_delete_on_termination():
+    ec2_client = boto3.resource('ec2', region_name='us-west-1')
+    result = ec2_client.create_instances(ImageId='ami-12345678', MinCount=1, MaxCount=1)
+    instance = result[0]
+    instance.load()
+    instance.block_device_mappings[0]['Ebs']['DeleteOnTermination'].should.be(False)
+    instance.modify_attribute(
+        BlockDeviceMappings=[{
+            'DeviceName': '/dev/sda1',
+            'Ebs': {'DeleteOnTermination': True}
+        }]
+    )
+    instance.load()
+    instance.block_device_mappings[0]['Ebs']['DeleteOnTermination'].should.be(True)