diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
--- a/clang/CMakeLists.txt
+++ b/clang/CMakeLists.txt
@@ -462,9 +462,6 @@
 
 option(CLANG_ENABLE_PROTO_FUZZER "Build Clang protobuf fuzzer." OFF)
 
-option(CLANG_ROUND_TRIP_CC1_ARGS
-  "Round-trip command line arguments in -cc1." ${LLVM_ENABLE_ASSERTIONS})
-
 if(NOT CLANG_ENABLE_STATIC_ANALYZER AND CLANG_ENABLE_ARCMT)
   message(FATAL_ERROR "Cannot disable static analyzer while enabling ARCMT or Z3")
 endif()
@@ -473,10 +470,6 @@
   set(CLANG_ENABLE_OBJC_REWRITER ON)
 endif()
 
-if (CLANG_ROUND_TRIP_CC1_ARGS)
-  add_definitions(-DCLANG_ROUND_TRIP_CC1_ARGS=ON)
-endif()
-
 # Clang version information
 set(CLANG_EXECUTABLE_VERSION
     "${CLANG_VERSION_MAJOR}" CACHE STRING
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -612,9 +612,8 @@
     CompilerInvocation::StringAllocator)>;
 
 // May perform round-trip of command line arguments. By default, the round-trip
-// is enabled if CLANG_ROUND_TRIP_CC1_ARGS was defined during build. This can be
-// overwritten at run-time via the "-round-trip-args" and "-no-round-trip-args"
-// command line flags.
+// is enabled in assert builds. This can be overwritten at run-time via the
+// "-round-trip-args" and "-no-round-trip-args" command line flags.
 // During round-trip, the command line arguments are parsed into a dummy
 // instance of CompilerInvocation which is used to generate the command line
 // arguments again. The real CompilerInvocation instance is then created by
@@ -624,8 +623,7 @@
                       CompilerInvocation &DummyInvocation,
                       ArrayRef<const char *> CommandLineArgs,
                       DiagnosticsEngine &Diags, const char *Argv0) {
-  // FIXME: Switch to '#ifndef NDEBUG' when possible.
-#ifdef CLANG_ROUND_TRIP_CC1_ARGS
+#ifndef NDEBUG
   bool DoRoundTripDefault = true;
 #else
   bool DoRoundTripDefault = false;