diff --git a/openbr/plugins/gui.cpp b/openbr/plugins/gui.cpp
index 526a480..d7bdd74 100644
--- a/openbr/plugins/gui.cpp
+++ b/openbr/plugins/gui.cpp
@@ -447,7 +447,8 @@ public:
             }
             emit this->changeTitle(newTitle);
 
-            foreach(const cv::Mat & m, t) {
+            foreach (const cv::Mat &m, t) {
+                if (!m.data) continue;
                 qImageBuffer = toQImage(m);
                 displayBuffer->convertFromImage(qImageBuffer);
 
diff --git a/openbr/plugins/slidingwindow.cpp b/openbr/plugins/slidingwindow.cpp
index 8063f46..458f681 100644
--- a/openbr/plugins/slidingwindow.cpp
+++ b/openbr/plugins/slidingwindow.cpp
@@ -270,6 +270,7 @@ class Detector : public Transform
     {
         const float aspectRatio = getAspectRatio(data);
         TemplateList cropped = cropTrainingSamples(data, aspectRatio);
+        qDebug("Detector using: %d training samples.", cropped.size());
         cropped.first().file.set("aspectRatio", aspectRatio);
         transform->train(cropped);
     }