diff --git a/builder/builder.sh b/builder/builder.sh
index 3ab339f7..5c7177ea 100644
--- a/builder/builder.sh
+++ b/builder/builder.sh
@@ -56,6 +56,10 @@ plugins() {
     mkdir -p /plugins
     for plugin in $(echo $PLUGINS | tr "," " "); do \
         import_package=$(get_package $plugin)
+        if [ -z "$import_package" ]; then
+            echo "Could not determine package for plugin $plugin"
+            return 1
+        fi
         $go_mod || go get -v "$import_package" ; # not needed for modules
         $go_mod && package="main" || package="caddyhttp"
         printf "package $package\nimport _ \"$import_package\"" > \