diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index d4c83272b74d0cd2408d7cb7273fa985f83b18fb..a6879379a219b2965297e8986564923f8e5ebc70 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1806,7 +1806,6 @@ static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
   Opts.NoBitFieldTypeAlign = Args.hasArg(OPT_fno_bitfield_type_align);
   Opts.SinglePrecisionConstants = Args.hasArg(OPT_cl_single_precision_constant);
   Opts.FastRelaxedMath = Args.hasArg(OPT_cl_fast_relaxed_math);
-  Opts.OptimizeSize = 0;
   Opts.MRTD = Args.hasArg(OPT_mrtd);
   Opts.FakeAddressSpaceMap = Args.hasArg(OPT_ffake_address_space_map);
   Opts.ParseUnknownAnytype = Args.hasArg(OPT_funknown_anytype);
@@ -1823,6 +1822,7 @@ static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
   // FIXME: Eliminate this dependency.
   unsigned Opt = getOptimizationLevel(Args, IK, Diags);
   Opts.Optimize = Opt != 0;
+  Opts.OptimizeSize = Args.hasArg(OPT_Os) || Args.hasArg(OPT_Oz);
 
   // This is the __NO_INLINE__ define, which just depends on things like the
   // optimization level and -fno-inline, not actually whether the backend has
diff --git a/clang/test/Preprocessor/optimize.c b/clang/test/Preprocessor/optimize.c
index c820ded909f763802e1b8c68759baa30503ea3e8..97f841a6fbb9d1ea0ab1b92d1e0990542d90eb27 100644
--- a/clang/test/Preprocessor/optimize.c
+++ b/clang/test/Preprocessor/optimize.c
@@ -23,7 +23,7 @@
   #ifndef __OPTIMIZE__
     #error "__OPTIMIZE__ not defined"
   #endif
-  #ifdef __OPTIMIZE_SIZE__
+  #ifndef __OPTIMIZE_SIZE__
     #error "__OPTIMIZE_SIZE__ not defined"
   #endif
 #endif