diff --git a/INSTALL.md b/INSTALL.md
index 0fdef238e..386d6afd3 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -37,9 +37,10 @@ Build dependencies are:
 Mapnik Core depends on:
 
  * Boost
-    - >= 1.47 is recommended
-    - >= 1.45.x is required if compiling with clang++
-    - >= 1.42.x works on most systems and most compilers
+    - >= 1.46 is recommended
+    - >= 1.45 is required if compiling with clang++
+    - >= 1.42 works on most systems and most compilers
+    - >= 1.47 is required to support wkt/wkb geometry output (optional)
     - These libraries are required:
       - filesystem
       - system