diff --git a/scripts/config_version.sh b/scripts/config_version.sh
index 0378952..7ccd2f4 100755
--- a/scripts/config_version.sh
+++ b/scripts/config_version.sh
@@ -1,5 +1,10 @@
 #!/bin/sh
 
+if [ $# -ne 2 -o ! -d "$1" -o ! -d "$1/$2" ]; then
+  echo "usage: $0 <environmentpath> <environment>" >&2
+  exit 1
+fi
+
 ruby=ruby
 script="$1/$2/scripts/config_version.rb"