diff --git a/Library/Homebrew/compat.rb b/Library/Homebrew/compat.rb
index d829e900cbdb9..6c3fa2dbba6d8 100644
--- a/Library/Homebrew/compat.rb
+++ b/Library/Homebrew/compat.rb
@@ -3,6 +3,7 @@
 require "compat/hbc"
 require "compat/formula"
 require "compat/formula_specialties"
+require "compat/formula_support"
 require "compat/global"
 require "compat/hardware"
 require "compat/macos"
diff --git a/Library/Homebrew/compat/dependency_collector.rb b/Library/Homebrew/compat/dependency_collector.rb
index 1c91f22830ea5..84d5431f3e8b6 100644
--- a/Library/Homebrew/compat/dependency_collector.rb
+++ b/Library/Homebrew/compat/dependency_collector.rb
@@ -1,80 +1,82 @@
 require "dependency_collector"
 
 class DependencyCollector
-  alias _parse_string_spec parse_string_spec
+  module Compat
+    # Define the languages that we can handle as external dependencies.
+    LANGUAGE_MODULES = Set[
+      :lua, :lua51, :perl, :python, :python3, :ruby
+    ].freeze
 
-  # Define the languages that we can handle as external dependencies.
-  LANGUAGE_MODULES = Set[
-    :lua, :lua51, :perl, :python, :python3, :ruby
-  ].freeze
+    def parse_string_spec(spec, tags)
+      if (tag = tags.first) && LANGUAGE_MODULES.include?(tag)
+        odeprecated "'depends_on ... => #{tag.inspect}'"
+        LanguageModuleRequirement.new(tag, spec, tags[1])
+      else
+        super
+      end
+    end
 
-  def parse_string_spec(spec, tags)
-    if (tag = tags.first) && LANGUAGE_MODULES.include?(tag)
-      odeprecated "'depends_on :#{tag}'"
-      LanguageModuleRequirement.new(tag, spec, tags[1])
-    else
-      _parse_string_spec(spec, tags)
+    def parse_symbol_spec(spec, tags)
+      case spec
+      when :clt
+        odeprecated "'depends_on :clt'"
+      when :tex
+        odeprecated "'depends_on :tex'"
+        TeXRequirement.new(tags)
+      when :autoconf, :automake, :bsdmake, :libtool
+        output_deprecation(spec)
+        autotools_dep(spec, tags)
+      when :cairo, :fontconfig, :freetype, :libpng, :pixman
+        output_deprecation(spec)
+        Dependency.new(spec.to_s, tags)
+      when :ant, :expat
+        output_deprecation(spec)
+        Dependency.new(spec.to_s, tags)
+      when :libltdl
+        tags << :run
+        output_deprecation("libtool")
+        Dependency.new("libtool", tags)
+      when :apr
+        output_deprecation(spec, "apr-util")
+        Dependency.new("apr-util", tags)
+      when :fortran
+        output_deprecation(spec, "gcc")
+        Dependency.new("gcc", tags)
+      when :gpg
+        output_deprecation(spec, "gnupg")
+        Dependency.new("gnupg", tags)
+      when :hg
+        output_deprecation(spec, "mercurial")
+        Dependency.new("mercurial", tags)
+      when :mpi
+        output_deprecation(spec, "open-mpi")
+        Dependency.new("open-mpi", tags)
+      when :python, :python2
+        output_deprecation(spec, "python")
+        Dependency.new("python", tags)
+      when :python3
+        output_deprecation(spec, "python3")
+        Dependency.new("python3", tags)
+      when :emacs, :mysql, :perl, :postgresql, :rbenv, :ruby
+        output_deprecation(spec)
+        Dependency.new(spec, tags)
+      else
+        super
+      end
     end
-  end
 
-  alias _parse_symbol_spec parse_symbol_spec
+    private
 
-  def parse_symbol_spec(spec, tags)
-    case spec
-    when :clt
-      odeprecated "'depends_on :clt'"
-    when :tex
-      odeprecated "'depends_on :tex'"
-      TeXRequirement.new(tags)
-    when :autoconf, :automake, :bsdmake, :libtool
-      output_deprecation(spec)
-      autotools_dep(spec, tags)
-    when :cairo, :fontconfig, :freetype, :libpng, :pixman
-      output_deprecation(spec)
-      Dependency.new(spec.to_s, tags)
-    when :ant, :expat
-      output_deprecation(spec)
+    def autotools_dep(spec, tags)
+      tags << :build unless tags.include? :run
       Dependency.new(spec.to_s, tags)
-    when :libltdl
-      tags << :run
-      output_deprecation("libtool")
-      Dependency.new("libtool", tags)
-    when :apr
-      output_deprecation(spec, "apr-util")
-      Dependency.new("apr-util", tags)
-    when :fortran
-      output_deprecation(spec, "gcc")
-      Dependency.new("gcc", tags)
-    when :gpg
-      output_deprecation(spec, "gnupg")
-      Dependency.new("gnupg", tags)
-    when :hg
-      output_deprecation(spec, "mercurial")
-      Dependency.new("mercurial", tags)
-    when :mpi
-      output_deprecation(spec, "open-mpi")
-      Dependency.new("open-mpi", tags)
-    when :python, :python2
-      output_deprecation(spec, "python")
-      Dependency.new("python", tags)
-    when :python3
-      output_deprecation(spec, "python3")
-      Dependency.new("python3", tags)
-    when :emacs, :mysql, :perl, :postgresql, :rbenv, :ruby
-      output_deprecation(spec)
-      Dependency.new(spec, tags)
-    else
-      _parse_symbol_spec(spec, tags)
     end
-  end
 
-  def autotools_dep(spec, tags)
-    tags << :build unless tags.include? :run
-    Dependency.new(spec.to_s, tags)
+    def output_deprecation(dependency, new_dependency = dependency)
+      odeprecated "'depends_on :#{dependency}'",
+                  "'depends_on \"#{new_dependency}\"'"
+    end
   end
 
-  def output_deprecation(dependency, new_dependency = dependency)
-    odeprecated "'depends_on :#{dependency}'",
-                "'depends_on \"#{new_dependency}\"'"
-  end
+  prepend Compat
 end
diff --git a/Library/Homebrew/compat/formula_support.rb b/Library/Homebrew/compat/formula_support.rb
index f56a4909b3ff9..9cb8d8ff144b4 100644
--- a/Library/Homebrew/compat/formula_support.rb
+++ b/Library/Homebrew/compat/formula_support.rb
@@ -1,18 +1,20 @@
 require "formula_support"
 
 class KegOnlyReason
-  alias _to_s to_s
+  module Compat
+    def to_s
+      case @reason
+      when :provided_by_osx
+        odeprecated "keg_only :provided_by_osx", "keg_only :provided_by_macos"
+        @reason = :provided_by_macos
+      when :shadowed_by_osx
+        odeprecated "keg_only :shadowed_by_osx", "keg_only :shadowed_by_macos"
+        @reason = :shadowed_by_macos
+      end
 
-  def to_s
-    case @reason
-    when :provided_by_osx
-      odeprecated "keg_only :provided_by_osx", "keg_only :provided_by_macos"
-      @reason = :provided_by_macos
-    when :shadowed_by_osx
-      odeprecated "keg_only :shadowed_by_osx", "keg_only :shadowed_by_macos"
-      @reason = :shadowed_by_macos
+      super
     end
-
-    _to_s
   end
+
+  prepend Compat
 end
diff --git a/Library/Homebrew/test/dependency_collector_spec.rb b/Library/Homebrew/test/dependency_collector_spec.rb
index 0f182a69e9211..46e859b2d8ae2 100644
--- a/Library/Homebrew/test/dependency_collector_spec.rb
+++ b/Library/Homebrew/test/dependency_collector_spec.rb
@@ -128,5 +128,15 @@ def find_requirement(klass)
       resource.download_strategy = Class.new
       expect { subject.add(resource) }.to raise_error(TypeError)
     end
+
+    it "is deprecated when called with a language module", :needs_compat do
+      expect(subject).to receive(:odeprecated)
+      subject.add("lpeg" => :lua)
+    end
+
+    it "is deprecated when called with deprecated requirements", :needs_compat do
+      expect(subject).to receive(:odeprecated)
+      subject.add(:python)
+    end
   end
 end
diff --git a/Library/Homebrew/test/formula_support_spec.rb b/Library/Homebrew/test/formula_support_spec.rb
index f42d61ba9bfab..7239ef352a6d4 100644
--- a/Library/Homebrew/test/formula_support_spec.rb
+++ b/Library/Homebrew/test/formula_support_spec.rb
@@ -3,7 +3,7 @@
 describe KegOnlyReason do
   describe "#to_s" do
     it "returns the reason provided" do
-      r = KegOnlyReason.new :provided_by_osx, "test"
+      r = KegOnlyReason.new :provided_by_macos, "test"
       expect(r.to_s).to eq("test")
     end
 
@@ -11,6 +11,12 @@
       r = KegOnlyReason.new :provided_by_macos, ""
       expect(r.to_s).to match(/^macOS already provides/)
     end
+
+    it "is deprecated when reason mentions 'osx'", :needs_compat do
+      r = KegOnlyReason.new :provided_by_osx, "test"
+      expect(r).to receive(:odeprecated)
+      r.to_s
+    end
   end
 end