diff -ur a/facedetect/meson.build b/facedetect/meson.build
--- a/facedetect/meson.build	2020-01-03 19:21:58.000000000 +0100
+++ b/facedetect/meson.build	2020-01-20 11:25:25.734556612 +0100
@@ -1,6 +1,6 @@
 subproject = ('facedetect')
 add_languages('cpp')
-facedetect_dep = dependency('opencv', version : ['>= 2.3.0'], required : true)
+facedetect_dep = dependency('opencv4', version : ['>= 2.3.0'], required : true)
 executable('shotwell-facedetect',
            'shotwell-facedetect.cpp',
            dependencies : facedetect_dep,
diff -ur a/facedetect/shotwell-facedetect.cpp b/facedetect/shotwell-facedetect.cpp
--- a/facedetect/shotwell-facedetect.cpp	2020-01-03 19:21:58.000000000 +0100
+++ b/facedetect/shotwell-facedetect.cpp	2020-01-20 11:22:17.208835929 +0100
@@ -10,6 +10,7 @@
 #include "opencv2/objdetect/objdetect.hpp"
 #include "opencv2/highgui/highgui.hpp"
 #include "opencv2/imgproc/imgproc.hpp"
+#include "opencv2/imgproc/types_c.h"
 
 #include <iostream>
 #include <stdio.h>
@@ -43,7 +44,7 @@
 	equalizeHist(smallImg, smallImg);
 
 	vector<Rect> faces;
-	cascade.detectMultiScale(smallImg, faces, 1.1, 2, CV_HAAR_SCALE_IMAGE, Size(30, 30));
+	cascade.detectMultiScale(smallImg, faces, 1.1, 2, cv::CASCADE_SCALE_IMAGE, cv::Size(30, 30));
 
 	int i = 0;
 	for (vector<Rect>::const_iterator r = faces.begin(); r != faces.end(); r++, i++) {
@@ -117,7 +118,7 @@
 
 	}
 
-	Mat image = imread(inputName, 1);
+	cv::Mat image = cv::imread(inputName, 1);
 
 	if (image.empty()) {