diff --git a/Library/Homebrew/os/mac/pkgconfig/10.13/zlib.pc b/Library/Homebrew/os/mac/pkgconfig/10.13/zlib.pc
index 6288921586..837bb70ac3 100644
--- a/Library/Homebrew/os/mac/pkgconfig/10.13/zlib.pc
+++ b/Library/Homebrew/os/mac/pkgconfig/10.13/zlib.pc
@@ -6,7 +6,7 @@ includedir=${prefix}/include
 
 Name: zlib
 Description: zlib compression library
-Version: 1.2.8
+Version: 1.2.11
 
 Requires:
 Libs: -L${libdir} -L${sharedlibdir} -lz
diff --git a/Library/Homebrew/os/mac/xcode.rb b/Library/Homebrew/os/mac/xcode.rb
index ec38512e80..e23a7cf3d9 100644
--- a/Library/Homebrew/os/mac/xcode.rb
+++ b/Library/Homebrew/os/mac/xcode.rb
@@ -216,7 +216,7 @@ module OS
         # on the older supported platform for that Xcode release, i.e there's no
         # CLT package for 10.11 that contains the Clang version from Xcode 8.
         case MacOS.version
-        when "10.13" then "900.0.28.1"
+        when "10.13" then "900.0.31"
         when "10.12" then "802.0.42"
         when "10.11" then "800.0.42.1"
         when "10.10" then "700.1.81"