diff --git a/graphdriver/devmapper/deviceset.go b/graphdriver/devmapper/deviceset.go
index 3dedfd75b5..c1f2f558a0 100644
--- a/graphdriver/devmapper/deviceset.go
+++ b/graphdriver/devmapper/deviceset.go
@@ -847,6 +847,9 @@ func (devices *DeviceSet) UnmountDevice(hash string, mode UnmountMode) error {
 	defer devices.Unlock()
 
 	info := devices.Devices[hash]
+	if info == nil {
+		return fmt.Errorf("UnmountDevice: no such device %s\n", hash)
+	}
 
 	if mode == UnmountFloat {
 		if info.floating {