Index: clang/CMakeLists.txt
===================================================================
--- clang/CMakeLists.txt
+++ clang/CMakeLists.txt
@@ -247,6 +247,17 @@
 
 option(CLANG_DEFAULT_PIE_ON_LINUX "Default to -fPIE and -pie on Linux" OFF)
 
+# Manually handle default so we can change the meaning of a cached default.
+set(CLANG_ENABLE_OPAQUE_POINTERS "DEFAULT" CACHE STRING
+    "Enable opaque pointers by default")
+if(CLANG_ENABLE_OPAQUE_POINTERS STREQUAL "DEFAULT")
+  set(CLANG_ENABLE_OPAQUE_POINTERS_INTERNAL OFF)
+elseif(CLANG_ENABLE_OPAQUE_POINTERS)
+  set(CLANG_ENABLE_OPAQUE_POINTERS_INTERNAL ON)
+else()
+  set(CLANG_ENABLE_OPAQUE_POINTERS_INTERNAL OFF)
+endif()
+
 # TODO: verify the values against LangStandards.def?
 set(CLANG_DEFAULT_STD_C "" CACHE STRING
   "Default standard to use for C/ObjC code (IDENT from LangStandards.def, empty for platform default)")
Index: clang/include/clang/Config/config.h.cmake
===================================================================
--- clang/include/clang/Config/config.h.cmake
+++ clang/include/clang/Config/config.h.cmake
@@ -89,4 +89,7 @@
 /* Spawn a new process clang.exe for the CC1 tool invocation, when necessary */
 #cmakedefine01 CLANG_SPAWN_CC1
 
+/* Whether to enable opaque pointers by default */
+#cmakedefine01 CLANG_ENABLE_OPAQUE_POINTERS_INTERNAL
+
 #endif
Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -5507,7 +5507,7 @@
 defm opaque_pointers : BoolOption<"",
   "opaque-pointers",
   CodeGenOpts<"OpaquePointers">,
-  DefaultFalse,
+  Default<"CLANG_ENABLE_OPAQUE_POINTERS_INTERNAL">,
   PosFlag<SetTrue, [], "Enable">,
   NegFlag<SetFalse, [], "Disable">,
   BothFlags<[], " opaque pointers">>;