diff --git a/Library/Homebrew/extend/os/mac/diagnostic.rb b/Library/Homebrew/extend/os/mac/diagnostic.rb
index cef36ac8f9..799b9a512e 100644
--- a/Library/Homebrew/extend/os/mac/diagnostic.rb
+++ b/Library/Homebrew/extend/os/mac/diagnostic.rb
@@ -20,6 +20,7 @@ module Homebrew
           check_xcode_minimum_version
           check_clt_minimum_version
           check_if_xcode_needs_clt_installed
+          check_if_clt_needs_headers_installed
         ].freeze
       end
 
@@ -135,6 +136,17 @@ module Homebrew
         EOS
       end
 
+      def check_if_clt_needs_headers_installed
+        return unless MacOS::CLT.separate_header_package?
+        return if MacOS::CLT.headers_installed?
+
+        <<~EOS
+          The Command Line Tools header package must be installed on #{MacOS.version.pretty_name}.
+          The installer is located at:
+            #{MacOS::CLT::HEADER_PKG_PATH.sub(":macos_version", MacOS.version)}
+        EOS
+      end
+
       def check_for_other_package_managers
         ponk = MacOS.macports_or_fink
         return if ponk.empty?
diff --git a/Library/Homebrew/extend/os/mac/system_config.rb b/Library/Homebrew/extend/os/mac/system_config.rb
index 20f04c0abd..d92da157b1 100644
--- a/Library/Homebrew/extend/os/mac/system_config.rb
+++ b/Library/Homebrew/extend/os/mac/system_config.rb
@@ -39,6 +39,12 @@ class SystemConfig
       end
     end
 
+    def clt_headers
+      @clt_headers ||= if MacOS::CLT.headers_installed?
+        MacOS::CLT.headers_version
+      end
+    end
+
     def xquartz
       @xquartz ||= if MacOS::XQuartz.installed?
         "#{MacOS::XQuartz.version} => #{describe_path(MacOS::XQuartz.prefix)}"
@@ -49,6 +55,9 @@ class SystemConfig
       dump_generic_verbose_config(f)
       f.puts "macOS: #{MacOS.full_version}-#{kernel}"
       f.puts "CLT: #{clt ? clt : "N/A"}"
+      if MacOS::CLT.separate_header_package?
+        f.puts "CLT headers: #{clt_headers ? clt_headers : "N/A"}"
+      end
       f.puts "Xcode: #{xcode ? xcode : "N/A"}"
       f.puts "XQuartz: #{xquartz ? xquartz : "N/A"}"
     end
diff --git a/Library/Homebrew/os/mac/xcode.rb b/Library/Homebrew/os/mac/xcode.rb
index c8a1c40440..b8f0f4031f 100644
--- a/Library/Homebrew/os/mac/xcode.rb
+++ b/Library/Homebrew/os/mac/xcode.rb
@@ -196,9 +196,13 @@ module OS
 
       STANDALONE_PKG_ID = "com.apple.pkg.DeveloperToolsCLILeo".freeze
       FROM_XCODE_PKG_ID = "com.apple.pkg.DeveloperToolsCLI".freeze
-      MAVERICKS_PKG_ID = "com.apple.pkg.CLTools_Executables".freeze
+      # EXECUTABLE_PKG_ID now means two things:
+      # 1. The original Mavericks CLT package ID, and
+      # 2. The additional header package included in Mojave.
+      EXECUTABLE_PKG_ID = "com.apple.pkg.CLTools_Executables".freeze
       MAVERICKS_NEW_PKG_ID = "com.apple.pkg.CLTools_Base".freeze # obsolete
       PKG_PATH = "/Library/Developer/CommandLineTools".freeze
+      HEADER_PKG_PATH = "/Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_:macos_version.pkg".freeze
 
       # Returns true even if outdated tools are installed, e.g.
       # tools from Xcode 4.x on 10.9
@@ -206,6 +210,18 @@ module OS
         !version.null?
       end
 
+      def separate_header_package?
+        MacOS.version >= :mojave
+      end
+
+      def headers_installed?
+        if !separate_header_package?
+          installed?
+        else
+          headers_version == version
+        end
+      end
+
       def update_instructions
         if MacOS.version >= "10.9"
           <<~EOS
@@ -282,6 +298,18 @@ module OS
         end
       end
 
+      # Version string of the header package, which is a
+      # separate package as of macOS 10.14.
+      def headers_version
+        if !separate_header_package?
+          version
+        else
+          @header_version ||= MacOS.pkgutil_info(EXECUTABLE_PKG_ID)[/version: (.+)$/, 1]
+          return ::Version::NULL unless @header_version
+          ::Version.new(@header_version)
+        end
+      end
+
       def detect_version
         # CLT isn't a distinct entity pre-4.3, and pkgutil doesn't exist
         # at all on Tiger, so just count it as installed if Xcode is installed
@@ -290,7 +318,7 @@ module OS
         end
 
         version = nil
-        [MAVERICKS_PKG_ID, MAVERICKS_NEW_PKG_ID, STANDALONE_PKG_ID, FROM_XCODE_PKG_ID].each do |id|
+        [EXECUTABLE_PKG_ID, MAVERICKS_NEW_PKG_ID, STANDALONE_PKG_ID, FROM_XCODE_PKG_ID].each do |id|
           if MacOS.version >= :mavericks
             next unless File.exist?("#{PKG_PATH}/usr/bin/clang")
           end
diff --git a/Library/Homebrew/test/os/mac/diagnostic_spec.rb b/Library/Homebrew/test/os/mac/diagnostic_spec.rb
index 22cbd158f1..d04b592dfb 100644
--- a/Library/Homebrew/test/os/mac/diagnostic_spec.rb
+++ b/Library/Homebrew/test/os/mac/diagnostic_spec.rb
@@ -32,6 +32,19 @@ describe Homebrew::Diagnostic::Checks do
       .to match("Xcode alone is not sufficient on El Capitan")
   end
 
+  specify "#check_if_clt_needs_headers_installed" do
+    allow(MacOS).to receive(:version).and_return(OS::Mac::Version.new("10.14"))
+    allow(MacOS::CLT).to receive(:installed?).and_return(true)
+    allow(MacOS::CLT).to receive(:headers_installed?).and_return(false)
+
+    expect(subject.check_if_clt_needs_headers_installed)
+      .to match("The Command Line Tools header package must be installed on Mojave.")
+
+    allow(MacOS).to receive(:version).and_return(OS::Mac::Version.new("10.13"))
+    expect(subject.check_if_clt_needs_headers_installed)
+      .to be_nil
+  end
+
   specify "#check_homebrew_prefix" do
     # the integration tests are run in a special prefix
     expect(subject.check_homebrew_prefix)