diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index 21c3115d26..28061442e7 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -704,6 +704,7 @@ class FormulaInstaller
         @@locked << dep.to_formula
       end unless ignore_deps?
       @@locked.unshift(f)
+      @@locked.uniq!
       @@locked.each(&:lock)
       @hold_locks = true
     end