diff --git a/tools/main.cpp b/tools/main.cpp
index b85f62b..eafa162 100644
--- a/tools/main.cpp
+++ b/tools/main.cpp
@@ -119,6 +119,12 @@
         }
     }
 
+    if (command.empty())
+    {
+        usage(argv[0]);
+        exit(EXIT_FAILURE);
+    }
+
     /* They want to update the firmware. */
     if (command == "update")
     {