diff --git a/gst/audiofx/audiofxbaseiirfilter.c b/gst/audiofx/audiofxbaseiirfilter.c
index 1ce4d8bc77..93553e8fe9 100644
--- a/gst/audiofx/audiofxbaseiirfilter.c
+++ b/gst/audiofx/audiofxbaseiirfilter.c
@@ -372,16 +372,16 @@ gst_audio_fx_base_iir_filter_transform_ip (GstBaseTransform * base,
   if (GST_CLOCK_TIME_IS_VALID (stream_time))
     gst_object_sync_values (GST_OBJECT (filter), stream_time);
 
-  if (filter->a == NULL || filter->b == NULL) {
-    g_return_val_if_fail (filter->a != NULL
-        && filter->b != NULL, GST_FLOW_ERROR);
-    return GST_FLOW_ERROR;
-  }
-
   gst_buffer_map (buf, &map, GST_MAP_READWRITE);
   num_samples = map.size / GST_AUDIO_FILTER_BPS (filter);
 
   g_mutex_lock (&filter->lock);
+  if (filter->a == NULL || filter->b == NULL) {
+    g_warn_if_fail (filter->a != NULL && filter->b != NULL);
+    gst_buffer_unmap (buf, &map);
+    g_mutex_unlock (&filter->lock);
+    return GST_FLOW_ERROR;
+  }
   filter->process (filter, map.data, num_samples);
   g_mutex_unlock (&filter->lock);