diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index a5e87193..876d8b06 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -38,3 +38,5 @@
 - Dan Farmer
   Incorporating CellProfiler's Canny edge detector
 
+- Pieter Holtzhausen
+  Incorporating CellProfiler's Sobel edge detector