diff --git a/Library/Homebrew/cask_dependent.rb b/Library/Homebrew/cask_dependent.rb
index 88c97c8df5..73d0eb3117 100644
--- a/Library/Homebrew/cask_dependent.rb
+++ b/Library/Homebrew/cask_dependent.rb
@@ -17,11 +17,8 @@ class CaskDependent
     @cask.full_name
   end
 
-  def runtime_dependencies(ignore_missing: false)
-    recursive_dependencies(ignore_missing: ignore_missing).reject do |dependency|
-      tags = dependency.tags
-      tags.include?(:build) || tags.include?(:test)
-    end
+  def runtime_dependencies
+    deps.map { |deps| [deps, deps.to_formula.runtime_dependencies] }.flatten.uniq
   end
 
   def deps
diff --git a/Library/Homebrew/dependency.rb b/Library/Homebrew/dependency.rb
index 65bc7d02ca..aa5375112a 100644
--- a/Library/Homebrew/dependency.rb
+++ b/Library/Homebrew/dependency.rb
@@ -124,7 +124,6 @@ class Dependency
           expanded_deps << dep
         else
           next if @expand_stack.include? dep.name
-          next if dep.tags.include?(:build)
 
           expanded_deps.concat(expand(dep.to_formula, cache_key: cache_key, ignore_missing: ignore_missing, &block))
           expanded_deps << dep
diff --git a/Library/Homebrew/installed_dependents.rb b/Library/Homebrew/installed_dependents.rb
index a0dabc58b7..7977dea71d 100644
--- a/Library/Homebrew/installed_dependents.rb
+++ b/Library/Homebrew/installed_dependents.rb
@@ -51,7 +51,7 @@ module InstalledDependents
         dependent.missing_dependencies(hide: keg_names)
       when Cask::Cask
         # When checking for cask dependents, we don't care about missing or non-runtime dependencies
-        CaskDependent.new(dependent).runtime_dependencies(ignore_missing: true).map(&:to_formula)
+        CaskDependent.new(dependent).runtime_dependencies.map(&:to_formula)
       end
 
       required_kegs = required.map do |f|