Index: clang/include/clang/Driver/Options.td
===================================================================
--- clang/include/clang/Driver/Options.td
+++ clang/include/clang/Driver/Options.td
@@ -1919,7 +1919,7 @@
 // This option was originally misspelt "infinites" [sic].
 def : Flag<["-"], "fhonor-infinites">, Alias<fhonor_infinities>;
 def : Flag<["-"], "fno-honor-infinites">, Alias<fno_honor_infinities>;
-def frounding_math : Flag<["-"], "frounding-math">, Group<f_Group>, Flags<[CC1Option]>,
+def frounding_math : Flag<["-"], "frounding-math">, Group<f_Group>, Flags<[CC1Option, FC1Option]>,
   MarshallingInfoFlag<LangOpts<"RoundingMath">>,
   Normalizer<"makeFlagToValueNormalizer(llvm::RoundingMode::Dynamic)">;
 def fno_rounding_math : Flag<["-"], "fno-rounding-math">, Group<f_Group>, Flags<[CC1Option]>;
Index: clang/lib/Driver/ToolChains/Flang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Flang.cpp
+++ clang/lib/Driver/ToolChains/Flang.cpp
@@ -89,6 +89,7 @@
   bool SignedZeros = true;
   bool AssociativeMath = false;
   bool ReciprocalMath = false;
+  bool RoundingFPMath = false;
 
   if (const Arg *A = Args.getLastArg(options::OPT_ffp_contract)) {
     const StringRef Val = A->getValue();
@@ -150,6 +151,12 @@
     case options::OPT_fno_reciprocal_math:
       ReciprocalMath = false;
       break;
+    case options::OPT_frounding_math:
+      RoundingFPMath = true;
+      break;
+    case options::OPT_fno_rounding_math:
+      RoundingFPMath = false;
+      break;
     }
 
     // If we handled this option claim it
@@ -176,6 +183,9 @@
 
   if (ReciprocalMath)
     CmdArgs.push_back("-freciprocal-math");
+
+  if (RoundingFPMath)
+    CmdArgs.push_back("-frounding-math");
 }
 
 void Flang::ConstructJob(Compilation &C, const JobAction &JA,
Index: flang/include/flang/Common/MathOptionsBase.def
===================================================================
--- flang/include/flang/Common/MathOptionsBase.def
+++ flang/include/flang/Common/MathOptionsBase.def
@@ -38,4 +38,7 @@
 /// Allow division operations to be reassociated
 ENUM_MATHOPT(ReciprocalMath, unsigned, 1, 0)
 
+/// Do not assume default floating-point rounding behavior
+ENUM_MATHOPT(RoundingMath, unsigned, 1, 0)
+
 #undef ENUM_MATHOPT
Index: flang/include/flang/Frontend/LangOptions.def
===================================================================
--- flang/include/flang/Frontend/LangOptions.def
+++ flang/include/flang/Frontend/LangOptions.def
@@ -34,6 +34,8 @@
 LANGOPT(AssociativeMath, 1, false)
 /// Allow division operations to be reassociated
 LANGOPT(ReciprocalMath, 1, false)
+/// Do not assume default floating-point rounding behavior
+LANGOPT(RoundingMath, 1, false)
 
 #undef LANGOPT
 #undef ENUM_LANGOPT
Index: flang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- flang/lib/Frontend/CompilerInvocation.cpp
+++ flang/lib/Frontend/CompilerInvocation.cpp
@@ -735,6 +735,12 @@
     opts.ReciprocalMath = true;
   }
 
+  if (const llvm::opt::Arg *a =
+          args.getLastArg(clang::driver::options::OPT_frounding_math)) {
+    diags.Report(diagUnimplemented) << a->getOption().getName();
+    opts.RoundingMath = true;
+  }
+
   return true;
 }
 
@@ -965,5 +971,6 @@
       .setApproxFunc(langOptions.ApproxFunc)
       .setNoSignedZeros(langOptions.NoSignedZeros)
       .setAssociativeMath(langOptions.AssociativeMath)
-      .setReciprocalMath(langOptions.ReciprocalMath);
+      .setReciprocalMath(langOptions.ReciprocalMath)
+      .setRoundingMath(langOptions.RoundingMath);
 }
Index: flang/lib/Optimizer/Builder/FIRBuilder.cpp
===================================================================
--- flang/lib/Optimizer/Builder/FIRBuilder.cpp
+++ flang/lib/Optimizer/Builder/FIRBuilder.cpp
@@ -619,6 +619,7 @@
   if (options.getReciprocalMath()) {
     arithFMF = arithFMF | mlir::arith::FastMathFlags::arcp;
   }
+  // TODO: getRoundingMath()
   setFastMathFlags(arithFMF);
 }
 
Index: flang/test/Driver/flang_fp_opts.f90
===================================================================
--- flang/test/Driver/flang_fp_opts.f90
+++ flang/test/Driver/flang_fp_opts.f90
@@ -8,6 +8,7 @@
 ! RUN:      -fno-signed-zeros \
 ! RUN:      -mreassociate \
 ! RUN:      -freciprocal-math \
+! RUN:      -frounding-math \
 ! RUN:      %s 2>&1 | FileCheck %s
 ! CHECK: ffp-contract= is not currently implemented
 ! CHECK: menable-no-infs is not currently implemented
@@ -16,3 +17,4 @@
 ! CHECK: fno-signed-zeros is not currently implemented
 ! CHECK: mreassociate is not currently implemented
 ! CHECK: freciprocal-math is not currently implemented
+! CHECK: frounding-math is not currently implemented
Index: flang/test/Driver/frontend-forwarding.f90
===================================================================
--- flang/test/Driver/frontend-forwarding.f90
+++ flang/test/Driver/frontend-forwarding.f90
@@ -15,6 +15,7 @@
 ! RUN:     -fno-signed-zeros \
 ! RUN:     -fassociative-math \
 ! RUN:     -freciprocal-math \
+! RUN:     -frounding-math \
 ! RUN:     -fpass-plugin=Bye%pluginext \
 ! RUN:     -mllvm -print-before-all\
 ! RUN:     -P \
@@ -33,6 +34,7 @@
 ! CHECK: "-fno-signed-zeros"
 ! CHECK: "-mreassociate"
 ! CHECK: "-freciprocal-math"
+! CHECK: "-frounding-math"
 ! CHECK: "-fconvert=little-endian"
 ! CHECK: "-fpass-plugin=Bye
 ! CHECK: "-mllvm" "-print-before-all"