diff --git a/src/FaceRecognizer.cc b/src/FaceRecognizer.cc
index 238a6af..9a2dd69 100644
--- a/src/FaceRecognizer.cc
+++ b/src/FaceRecognizer.cc
@@ -162,7 +162,9 @@ Local<Value> UnwrapTrainingData(Nan::NAN_METHOD_ARGS_TYPE info,
     int label = valarr->Get(0)->Uint32Value();
     cv::Mat im = fromMatrixOrFilename(valarr->Get(1));
     im = im.clone();
-    cv::cvtColor(im, im, CV_RGB2GRAY);
+    if (im.channels() == 3) {
+      cv::cvtColor(im, im, CV_RGB2GRAY);
+    }
     labels->push_back(label);
     images->push_back(im);
   }