diff --git a/doc/51Degrees-device-detection.txt b/doc/51Degrees-device-detection.txt
index 381008a..2d4679d 100644
--- a/doc/51Degrees-device-detection.txt
+++ b/doc/51Degrees-device-detection.txt
@@ -53,6 +53,15 @@
 Trie data. Free Hash Trie data file can be obtained by signing up for a licence
 key at https://51degrees.com/products/store/on-premise-device-detection.
 
+For HAProxy developers who need to verify that their changes didn't affect the
+51Degrees implementation, a dummy library if provided in the contrib/51d
+directory. This does not function, but implements the API such that the
+51Degrees module can be used (but not return any meaningful information). To
+test either Pattern or Hash Trie, build with:
+    $ make TARGET=<target> USE_51DEGREES=1 51DEGREES_SRC=contrib/51d/pattern
+or
+    $ make TARGET=<target> USE_51DEGREES=1 51DEGREES_SRC=contrib/51d/trie
+respectively.
 
 The configuration file needs to set the following parameters: