diff --git a/.gitmodules b/.gitmodules
index d0ae1390c..281ddbda3 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -5,3 +5,4 @@
 [submodule "test/data-visual"]
 	path = test/data-visual
 	url = https://github.com/mapnik/test-data-visual.git
+	branch = master