diff --git a/argfilters.module b/argfilters.module
index 5331a6f..38eb380 100755
--- a/argfilters.module
+++ b/argfilters.module
@@ -16,14 +16,16 @@ function argfilters_views_query_substitutions() {
   // set.
   $replacements = array();
   if (is_array($view->argument)) {
-    foreach($view->argument as $index => $argument) {
+    foreach ($view->argument as $index => $argument) {
       // Shift all indeces up one step, to sync with the outward-facing
       // denumeration used in the Views interface.
-      $newindex = $index + 1;
-      $replacements["!$newindex"] = $argument->argument;
-      // TODO: Use $view->argument to load the validated title for the argument
-      // object, if there is any. For now, we only use the raw input value.
-      $replacements["%$newindex"] = $argument->argument;
+      if (is_numeric($index)) {
+        $newindex = $index + 1;
+        $replacements["!$newindex"] = $argument->argument;
+        // TODO: Use $view->argument to load the validated title for the argument
+        // object, if there is any. For now, we only use the raw input value.
+        $replacements["%$newindex"] = $argument->argument;
+      }
     }
   }