diff --git a/Library/Homebrew/cask_dependent.rb b/Library/Homebrew/cask_dependent.rb
index 73d0eb3117..9cad6a06f4 100644
--- a/Library/Homebrew/cask_dependent.rb
+++ b/Library/Homebrew/cask_dependent.rb
@@ -18,7 +18,7 @@ class CaskDependent
   end
 
   def runtime_dependencies
-    deps.map { |deps| [deps, deps.to_formula.runtime_dependencies] }.flatten.uniq
+    deps.flat_map { |dep| [dep, dep.to_formula.runtime_dependencies] }.uniq
   end
 
   def deps