--- a/drupal_apc_cache.inc
+++ b/drupal_apc_cache.inc
@@ -49,8 +49,12 @@
     $prefixes = variable_get('cache_prefix', '');
 
     if (is_string($prefixes)) {
-      // Variable can be a string, which then considered as a default behavior.
-      return $prefixes;
+      if ($prefixes != '') {
+        // Variable can be a string, which then considered as a default behavior.
+        return $prefixes;
+      } else {
+        return getcwd();
+      }
     }
 
     if (isset($prefixes[$bin])) {