diff --git a/Library/Homebrew/diagnostic.rb b/Library/Homebrew/diagnostic.rb
index a5b1302bdee01..b434c394bddad 100644
--- a/Library/Homebrew/diagnostic.rb
+++ b/Library/Homebrew/diagnostic.rb
@@ -8,27 +8,13 @@
 module Homebrew
   module Diagnostic
     def self.missing_deps(ff, hide = nil)
-      hide ||= []
-
       missing = {}
       ff.each do |f|
-        missing_deps = f.recursive_dependencies do |dependent, dep|
-          if dep.optional? || dep.recommended?
-            tab = Tab.for_formula(dependent)
-            Dependency.prune unless tab.with?(dep)
-          elsif dep.build?
-            Dependency.prune
-          end
-        end
-
-        missing_deps.map!(&:to_formula)
-        missing_deps.reject! do |d|
-          !hide.include?(d.name) && d.installed_prefixes.any?
-        end
+        missing_dependencies = f.missing_dependencies(hide: hide)
 
-        unless missing_deps.empty?
-          yield f.full_name, missing_deps if block_given?
-          missing[f.full_name] = missing_deps
+        unless missing_dependencies.empty?
+          yield f.full_name, missing_dependencies if block_given?
+          missing[f.full_name] = missing_dependencies
         end
       end
       missing
diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index c2467b7bce3e2..947313047473f 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -1466,6 +1466,26 @@ def runtime_dependencies
     recursive_dependencies.reject(&:build?)
   end
 
+  # Returns a list of formulae depended on by this formula that aren't
+  # installed
+  def missing_dependencies(hide: nil)
+    hide ||= []
+    missing_dependencies = recursive_dependencies do |dependent, dep|
+      if dep.optional? || dep.recommended?
+        tab = Tab.for_formula(dependent)
+        Dependency.prune unless tab.with?(dep)
+      elsif dep.build?
+        Dependency.prune
+      end
+    end
+
+    missing_dependencies.map!(&:to_formula)
+    missing_dependencies.select! do |d|
+      hide.include?(d.name) || d.installed_prefixes.empty?
+    end
+    missing_dependencies
+  end
+
   # @private
   def to_hash
     hsh = {