diff --git a/BUILDING.txt b/BUILDING.txt
index 662bd2577a3..c4252d757b9 100644
--- a/BUILDING.txt
+++ b/BUILDING.txt
@@ -8,7 +8,7 @@ Requirements:
 * Maven 3.0
 * Forrest 0.8 (if generating docs)
 * Findbugs 1.3.9 (if running findbugs)
-* ProtocolBuffer 2.4.1+ (for MapReduce)
+* ProtocolBuffer 2.4.1+ (for MapReduce and HDFS)
 * Autotools (if compiling native code)
 * Internet connection for first build (to fetch all Maven and Hadoop dependencies)