diff --git a/Library/Formula/monotone.rb b/Library/Formula/monotone.rb
index cb5183cc8be5..79af0fc6f276 100644
--- a/Library/Formula/monotone.rb
+++ b/Library/Formula/monotone.rb
@@ -39,10 +39,14 @@ def install
     # building boost (which takes approximately forever) if it's not already installed.
     # This is suggested in the Monotone installation instructions.
 
+    boost_prefix = buildpath/'boost'
     boost = Formula.factory('boost')
     unless boost.installed?
-      # Add header location to CPPFLAGS
-      boost.brew { ENV.append "CPPFLAGS", "-I#{buildpath}" }
+      boost.brew do
+        boost_prefix.install Dir['*']
+        # Add header location to CPPFLAGS
+        ENV.append 'CPPFLAGS', "-I#{boost_prefix}"
+      end
     end
 
     system "./configure", "--disable-dependency-tracking",