diff --git a/README.md b/README.md
index 900cd72..e3e8582 100644
--- a/README.md
+++ b/README.md
@@ -69,3 +69,6 @@ make -j8
 ## Licence
 The code is provided under a BSD 3-clause license. See the LICENSE file for details.
 Note also the different licenses of thirdparty submodules.
+
+Some improvements are ported back from the fork
+[granite](https://github.com/DLR-RM/granite) (MIT license).
diff --git a/include/basalt/optical_flow/multiscale_frame_to_frame_optical_flow.h b/include/basalt/optical_flow/multiscale_frame_to_frame_optical_flow.h
index 8fdabff..5fda7f8 100644
--- a/include/basalt/optical_flow/multiscale_frame_to_frame_optical_flow.h
+++ b/include/basalt/optical_flow/multiscale_frame_to_frame_optical_flow.h
@@ -33,6 +33,9 @@ OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
 
+// Original source for multi-scale implementation:
+// https://github.com/DLR-RM/granite (MIT license)
+
 #pragma once
 
 #include <thread>