diff --git a/contrib/search_api_facetapi/plugins/facetapi/query_type_term.inc b/contrib/search_api_facetapi/plugins/facetapi/query_type_term.inc
index 4341133..587a37f 100644
--- a/contrib/search_api_facetapi/plugins/facetapi/query_type_term.inc
+++ b/contrib/search_api_facetapi/plugins/facetapi/query_type_term.inc
@@ -70,7 +70,7 @@ class SearchApiFacetapiTerm extends FacetapiQueryType implements FacetapiQueryTy
     if ($filter == '!') {
       $query_filter->condition($field, NULL);
     }
-    elseif ($filter[0] == '[' && $filter[strlen($filter) - 1] == ']' && ($pos = strpos($filter, ' TO '))) {
+    elseif ($filter && $filter[0] == '[' && $filter[strlen($filter) - 1] == ']' && ($pos = strpos($filter, ' TO '))) {
       $lower = trim(substr($filter, 1, $pos));
       $upper = trim(substr($filter, $pos + 4, -1));
       if ($lower == '*' && $upper == '*') {