diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index a2768f7a10..bd341c365e 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -158,6 +158,22 @@ class FormulaInstaller
       check_infopages
       check_m4
     end
+
+    keg = Keg.new(f.prefix)
+
+    if keg.completion_installed? :bash
+      ohai 'Caveats', <<-EOS.undent
+        Bash completion has been installed to:
+          #{HOMEBREW_PREFIX}/etc/bash_completion.d
+        EOS
+    end
+
+    if keg.completion_installed? :zsh
+      ohai 'Caveats', <<-EOS.undent
+        zsh completion has been installed to:
+          #{HOMEBREW_PREFIX}/share/zsh/site-functions
+        EOS
+    end
   end
 
   def finish
diff --git a/Library/Homebrew/keg.rb b/Library/Homebrew/keg.rb
index 269999bc3d..dae91ea1d7 100644
--- a/Library/Homebrew/keg.rb
+++ b/Library/Homebrew/keg.rb
@@ -58,6 +58,15 @@ class Keg < Pathname
     linked_keg_record.directory? and self == linked_keg_record.realpath
   end
 
+  def completion_installed? shell
+    dir = case shell
+      when :bash then self/'etc/bash_completion.d'
+      when :zsh then self/'share/zsh/site-functions'
+      end
+    return if dir.nil?
+    dir.directory? and not dir.children.length.zero?
+  end
+
   def link mode=nil
     raise "Cannot link #{fname}\nAnother version is already linked: #{linked_keg_record.realpath}" if linked_keg_record.directory?