diff --git a/plugin.sh b/plugin.sh
index 531fbcd..12d0113 100755
--- a/plugin.sh
+++ b/plugin.sh
@@ -2,6 +2,8 @@
 
 set -ex
 
+PLUGIN_COMMAND=${PLUGIN_COMMAND:?command is not set}
+
 ABRA=/root/.local/bin/abra
 
 output_versions(){