diff --git a/dlib/svm/structural_object_detection_trainer_abstract.h b/dlib/svm/structural_object_detection_trainer_abstract.h
index 4cf351462..3373b4380 100644
--- a/dlib/svm/structural_object_detection_trainer_abstract.h
+++ b/dlib/svm/structural_object_detection_trainer_abstract.h
@@ -22,6 +22,8 @@ namespace dlib
         /*!
             REQUIREMENTS ON image_scanner_type
                 image_scanner_type must be an implementation of 
+                dlib/image_processing/scan_fhog_pyramid_abstract.h or
+                dlib/image_processing/scan_image_custom_abstract.h or
                 dlib/image_processing/scan_image_pyramid_abstract.h or
                 dlib/image_processing/scan_image_boxes_abstract.h
 
diff --git a/dlib/svm/structural_svm_object_detection_problem_abstract.h b/dlib/svm/structural_svm_object_detection_problem_abstract.h
index 6bb6c47a9..b7f8a3e36 100644
--- a/dlib/svm/structural_svm_object_detection_problem_abstract.h
+++ b/dlib/svm/structural_svm_object_detection_problem_abstract.h
@@ -41,6 +41,8 @@ namespace dlib
         /*!
             REQUIREMENTS ON image_scanner_type
                 image_scanner_type must be an implementation of 
+                dlib/image_processing/scan_fhog_pyramid_abstract.h or
+                dlib/image_processing/scan_image_custom_abstract.h or
                 dlib/image_processing/scan_image_pyramid_abstract.h or
                 dlib/image_processing/scan_image_boxes_abstract.h