diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -19,11 +19,13 @@
 #include "clang/Driver/Options.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
+#include "llvm/ADT/Triple.h"
 #include "llvm/Option/Arg.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Option/OptTable.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/FileUtilities.h"
+#include "llvm/Support/Host.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/raw_ostream.h"
@@ -93,7 +95,9 @@
 /// \param [in] opts The target options instance to update
 /// \param [in] args The list of input arguments (from the compiler invocation)
 static void ParseTargetArgs(TargetOptions &opts, llvm::opt::ArgList &args) {
-  opts.triple = args.getLastArgValue(clang::driver::options::OPT_triple);
+  if (const llvm::opt::Arg *a =
+          args.getLastArg(clang::driver::options::OPT_triple))
+    opts.triple = a->getValue();
 }
 
 // Tweak the frontend configuration based on the frontend action
@@ -559,6 +563,15 @@
 
   bool success = true;
 
+  // Set the default triple for this CompilerInvocation. This might be
+  // overridden by users with `-triple` (see the call to `ParseTargetArgs`
+  // below).
+  // NOTE: Like in Clang, it would be nice to use option marshalling
+  // for this so that the entire logic for setting-up the triple is in one
+  // place.
+  res.targetOpts().triple =
+      llvm::Triple::normalize(llvm::sys::getDefaultTargetTriple());
+
   // Parse the arguments
   const llvm::opt::OptTable &opts = clang::driver::getDriverOptTable();
   const unsigned includedFlagsBitmask = clang::driver::options::FC1Option;
diff --git a/flang/lib/Frontend/FrontendActions.cpp b/flang/lib/Frontend/FrontendActions.cpp
--- a/flang/lib/Frontend/FrontendActions.cpp
+++ b/flang/lib/Frontend/FrontendActions.cpp
@@ -30,6 +30,7 @@
 #include "mlir/IR/Dialect.h"
 #include "mlir/Pass/PassManager.h"
 #include "mlir/Target/LLVMIR/ModuleTranslation.h"
+#include "clang/Basic/DiagnosticFrontend.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
@@ -481,9 +482,15 @@
   if (!llvmModule)
     GenerateLLVMIR();
 
-  // Create and configure `Target`
+  // Set the triple based on the CompilerInvocation set-up
+  const std::string &theTriple = ci.invocation().targetOpts().triple;
+  if (llvmModule->getTargetTriple() != theTriple) {
+    ci.diagnostics().Report(clang::diag::warn_fe_override_module) << theTriple;
+    llvmModule->setTargetTriple(theTriple);
+  }
+
+  // Create `Target`
   std::string error;
-  std::string theTriple = llvmModule->getTargetTriple();
   const llvm::Target *theTarget =
       llvm::TargetRegistry::lookupTarget(theTriple, error);
   assert(theTarget && "Failed to create Target");
@@ -546,13 +553,17 @@
   if (!llvmModule)
     GenerateLLVMIR();
 
+  // Set the triple based on the CompilerInvocation set-up
+  const std::string &theTriple = ci.invocation().targetOpts().triple;
+  if (llvmModule->getTargetTriple() != theTriple) {
+    ci.diagnostics().Report(clang::diag::warn_fe_override_module) << theTriple;
+    llvmModule->setTargetTriple(theTriple);
+  }
+
   // Create `Target`
   std::string error;
-  const std::string &theTriple = llvmModule->getTargetTriple();
   const llvm::Target *theTarget =
       llvm::TargetRegistry::lookupTarget(theTriple, error);
-  // TODO: Make this a diagnostic once `flang-new` can consume LLVM IR files
-  // (in which users could use unsupported triples)
   assert(theTarget && "Failed to create Target");
 
   // Create `TargetMachine`
diff --git a/flang/unittests/Frontend/FrontendActionTest.cpp b/flang/unittests/Frontend/FrontendActionTest.cpp
--- a/flang/unittests/Frontend/FrontendActionTest.cpp
+++ b/flang/unittests/Frontend/FrontendActionTest.cpp
@@ -10,7 +10,9 @@
 #include "flang/Frontend/CompilerInvocation.h"
 #include "flang/Frontend/FrontendOptions.h"
 #include "flang/FrontendTool/Utils.h"
+#include "llvm/ADT/Triple.h"
 #include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Host.h"
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -170,7 +172,10 @@
 
   // Set-up the action kind.
   compInst_.invocation().frontendOpts().programAction = EmitLLVM;
-  compInst_.invocation().preprocessorOpts().noReformat = true;
+
+  // Set-up default target triple.
+  compInst_.invocation().targetOpts().triple =
+      llvm::Triple::normalize(llvm::sys::getDefaultTargetTriple());
 
   // Set-up the output stream. We are using output buffer wrapped as an output
   // stream, as opposed to an actual file (or a file descriptor).
@@ -197,7 +202,10 @@
 
   // Set-up the action kind.
   compInst_.invocation().frontendOpts().programAction = EmitAssembly;
-  compInst_.invocation().preprocessorOpts().noReformat = true;
+
+  // Set-up default target triple.
+  compInst_.invocation().targetOpts().triple =
+      llvm::Triple::normalize(llvm::sys::getDefaultTargetTriple());
 
   // Initialise LLVM backend
   llvm::InitializeAllTargets();