diff --git a/flang/include/flang/Frontend/FrontendAction.h b/flang/include/flang/Frontend/FrontendAction.h
--- a/flang/include/flang/Frontend/FrontendAction.h
+++ b/flang/include/flang/Frontend/FrontendAction.h
@@ -39,6 +39,12 @@
   /// By default it returns true if a compiler error occurred.
   virtual bool ShouldEraseOutputFiles();
 
+  /// Callback at the start of processing a single input.
+  ///
+  /// \return True on success; on failure ExecutionAction() and
+  /// EndSourceFileAction() will not be called.
+  virtual bool BeginSourceFileAction(CompilerInstance &ci) { return true; }
+
   /// @}
 
 public:
@@ -76,7 +82,7 @@
 
   /// @}
   /// @name Public Action Interface
-  /// @}
+  /// @{
 
   /// Prepare the action for processing the input file \p input.
   ///
diff --git a/flang/include/flang/Frontend/FrontendActions.h b/flang/include/flang/Frontend/FrontendActions.h
--- a/flang/include/flang/Frontend/FrontendActions.h
+++ b/flang/include/flang/Frontend/FrontendActions.h
@@ -21,15 +21,23 @@
   void ExecuteAction() override;
 };
 
-class PrintPreprocessedAction : public FrontendAction {
+class EmitObjAction : public FrontendAction {
   void ExecuteAction() override;
 };
 
-class ParseSyntaxOnlyAction : public FrontendAction {
+//===----------------------------------------------------------------------===//
+// Prescan Actions
+//===----------------------------------------------------------------------===//
+class PrescanAction : public FrontendAction {
   void ExecuteAction() override;
+  bool BeginSourceFileAction(CompilerInstance &ci) override;
 };
 
-class EmitObjAction : public FrontendAction {
+class PrintPreprocessedAction : public PrescanAction {
+  void ExecuteAction() override;
+};
+
+class ParseSyntaxOnlyAction : public PrescanAction {
   void ExecuteAction() override;
 };
 
diff --git a/flang/lib/Frontend/CompilerInstance.cpp b/flang/lib/Frontend/CompilerInstance.cpp
--- a/flang/lib/Frontend/CompilerInstance.cpp
+++ b/flang/lib/Frontend/CompilerInstance.cpp
@@ -148,12 +148,6 @@
   // Run the frontend action `act` for every input file.
   for (const FrontendInputFile &fif : frontendOpts().inputs_) {
     if (act.BeginSourceFile(*this, fif)) {
-      // Switch between fixed and free form format based on the input file
-      // extension. Ideally we should have all Fortran options set before
-      // entering this loop (i.e. processing any input files). However, we
-      // can't decide between fixed and free form based on the file extension
-      // earlier than this.
-      invoc.fortranOpts().isFixedForm = fif.IsFixedForm();
       if (llvm::Error err = act.Execute()) {
         consumeError(std::move(err));
       }
diff --git a/flang/lib/Frontend/FrontendAction.cpp b/flang/lib/Frontend/FrontendAction.cpp
--- a/flang/lib/Frontend/FrontendAction.cpp
+++ b/flang/lib/Frontend/FrontendAction.cpp
@@ -35,10 +35,17 @@
   assert(!realInput.IsEmpty() && "Unexpected empty filename!");
   set_currentInput(realInput);
   set_instance(&ci);
+
   if (!ci.HasAllSources()) {
     BeginSourceFileCleanUp(*this, ci);
     return false;
   }
+
+  if (!BeginSourceFileAction(ci)) {
+    BeginSourceFileCleanUp(*this, ci);
+    return false;
+  }
+
   return true;
 }
 
@@ -47,25 +54,6 @@
 }
 
 llvm::Error FrontendAction::Execute() {
-  CompilerInstance &ci = this->instance();
-
-  std::string currentInputPath{GetCurrentFileOrBufferName()};
-
-  Fortran::parser::Options parserOptions =
-      this->instance().invocation().fortranOpts();
-
-  // Prescan. In case of failure, report and return.
-  ci.parsing().Prescan(currentInputPath, parserOptions);
-
-  if (ci.parsing().messages().AnyFatalError()) {
-    const unsigned diagID = ci.diagnostics().getCustomDiagID(
-        clang::DiagnosticsEngine::Error, "Could not scan %0");
-    ci.diagnostics().Report(diagID) << GetCurrentFileOrBufferName();
-    ci.parsing().messages().Emit(llvm::errs(), ci.allCookedSources());
-
-    return llvm::Error::success();
-  }
-
   ExecuteAction();
 
   return llvm::Error::success();
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
@@ -16,8 +16,37 @@
 
 using namespace Fortran::frontend;
 
-void InputOutputTestAction::ExecuteAction() {
+bool PrescanAction::BeginSourceFileAction(CompilerInstance &c1) {
+  CompilerInstance &ci = this->instance();
+
+  std::string currentInputPath{GetCurrentFileOrBufferName()};
+
+  Fortran::parser::Options parserOptions =
+      this->instance().invocation().fortranOpts();
+
+  // Switch between fixed and free form format based on the input file
+  // extension. Ideally we should have all Fortran options set before
+  // entering this loop (i.e. processing any input files). However, we
+  // can't decide between fixed and free form based on the file extension
+  // earlier than this.
+  parserOptions.isFixedForm = currentInput().IsFixedForm();
+
+  // Prescan. In case of failure, report and return.
+  ci.parsing().Prescan(currentInputPath, parserOptions);
+
+  if (ci.parsing().messages().AnyFatalError()) {
+    const unsigned diagID = ci.diagnostics().getCustomDiagID(
+        clang::DiagnosticsEngine::Error, "Could not scan %0");
+    ci.diagnostics().Report(diagID) << GetCurrentFileOrBufferName();
+    ci.parsing().messages().Emit(llvm::errs(), ci.allCookedSources());
+
+    return false;
+  }
 
+  return true;
+}
+
+void InputOutputTestAction::ExecuteAction() {
   // Get the name of the file from FrontendInputFile current.
   std::string path{GetCurrentFileOrBufferName()};
   std::string buf;