diff --git a/moto/ec2/models.py b/moto/ec2/models.py
index 201754cf3..a8724e655 100644
--- a/moto/ec2/models.py
+++ b/moto/ec2/models.py
@@ -263,7 +263,7 @@ class Instance(BotoInstance, TaggedEC2Instance):
         self.key_name = kwargs.get("key_name")
 
         self.block_device_mapping = BlockDeviceMapping()
-        self.block_device_mapping['/dev/sda1'] = BlockDeviceType()
+        self.block_device_mapping['/dev/sda1'] = BlockDeviceType(volume_id=random_volume_id())
 
         amis = ec2_backend.describe_images(filters={'image-id': image_id})
         ami = amis[0] if amis else None
diff --git a/moto/ec2/responses/instances.py b/moto/ec2/responses/instances.py
index c92de014b..27625341d 100644
--- a/moto/ec2/responses/instances.py
+++ b/moto/ec2/responses/instances.py
@@ -340,7 +340,17 @@ EC2_DESCRIBE_INSTANCES = """<DescribeInstancesResponse xmlns='http://ec2.amazona
                     <kernelId>{{ instance.kernel }}</kernelId>
                     <rootDeviceType>ebs</rootDeviceType>
                     <rootDeviceName>/dev/sda1</rootDeviceName>
-                    <blockDeviceMapping />
+                    <blockDeviceMapping>
+                      <item>
+                        <deviceName>/dev/sda1</deviceName>
+                          <ebs>
+                            <volumeId>{{ instance.block_device_mapping['/dev/sda1'].volume_id }}</volumeId>
+                            <status>attached</status>
+                            <attachTime>YYYY-MM-DDTHH:MM:SS.SSSZ</attachTime>
+                            <deleteOnTermination>true</deleteOnTermination>
+                        </ebs>
+                      </item>
+                    </blockDeviceMapping>
                     <virtualizationType>{{ instance.virtualization_type }}</virtualizationType>
                     <clientToken>ABCDE1234567890123</clientToken>
                     <tagSet>
diff --git a/tests/test_ec2/test_instances.py b/tests/test_ec2/test_instances.py
index 910944ace..a65f3436f 100644
--- a/tests/test_ec2/test_instances.py
+++ b/tests/test_ec2/test_instances.py
@@ -50,6 +50,10 @@ def test_instance_launch_and_terminate():
     instances[0].id.should.equal(instance.id)
     instances[0].state.should.equal('running')
 
+    root_device_name = instances[0].root_device_name
+    instances[0].block_device_mapping[root_device_name].status.should.equal('attached')
+    instances[0].block_device_mapping[root_device_name].volume_id.should.match(r'vol-\w+')
+
     conn.terminate_instances([instances[0].id])
 
     reservations = conn.get_all_instances()