diff --git a/core/src/main/java/org/mapfish/print/test/util/ImageSimilarity.java b/core/src/main/java/org/mapfish/print/test/util/ImageSimilarity.java
index 3fd46adde1..6c564cc884 100644
--- a/core/src/main/java/org/mapfish/print/test/util/ImageSimilarity.java
+++ b/core/src/main/java/org/mapfish/print/test/util/ImageSimilarity.java
@@ -263,7 +263,15 @@ private File getRelatedFile(final String name) {
             squareDist += colorDist * colorDist;
           }
         } else if (maskPixel[0] != 0) {
-          throw new RuntimeException("Mask image must be only black and white (0 and 255)");
+          throw new RuntimeException(
+              "Mask image must be only black and white (0 and 255), got "
+                  + maskPixel[0]
+                  + " at "
+                  + x
+                  + ","
+                  + y
+                  + " in "
+                  + this.maskImage);
         }
         double pxDiff = Math.sqrt(squareDist / this.expectedImage.getSampleModel().getNumBands());
         dist += pxDiff / 255;
diff --git a/docker-compose.yaml b/docker-compose.yaml
index 11482361d1..85431071bc 100644
--- a/docker-compose.yaml
+++ b/docker-compose.yaml
@@ -25,6 +25,7 @@ services:
     user: ${USER_ID}
     command: tail --follow /dev/null
     volumes:
+      - ./examples/src:/src/examples/src:ro
       - ./examples/src/test/resources/examples:/src/examples/src/test/resources/examples
       - ./examples/build/reports:/src/examples/build/reports
       - ./examples/build/resources:/src/examples/build/resources
diff --git a/examples/src/test/resources/examples/datasource_multiple_maps/expected_output/mask-requestData.png b/examples/src/test/resources/examples/datasource_multiple_maps/expected_output/mask-requestData.png
index 358b3722a5..bfd6a4d8ea 100644
Binary files a/examples/src/test/resources/examples/datasource_multiple_maps/expected_output/mask-requestData.png and b/examples/src/test/resources/examples/datasource_multiple_maps/expected_output/mask-requestData.png differ
diff --git a/examples/src/test/resources/examples/simple/expected_output/requestData-fontawesome.png b/examples/src/test/resources/examples/simple/expected_output/requestData-fontawesome.png
index 1d3686bd1e..9fe760fe40 100644
Binary files a/examples/src/test/resources/examples/simple/expected_output/requestData-fontawesome.png and b/examples/src/test/resources/examples/simple/expected_output/requestData-fontawesome.png differ