diff --git a/flang/lib/Semantics/mod-file.h b/flang/lib/Semantics/mod-file.h
--- a/flang/lib/Semantics/mod-file.h
+++ b/flang/lib/Semantics/mod-file.h
@@ -32,11 +32,13 @@
 
 class ModFileWriter {
 public:
-  ModFileWriter(SemanticsContext &context) : context_{context} {}
+  ModFileWriter(SemanticsContext &);
+  ~ModFileWriter();
   bool WriteAll();
 
 private:
   SemanticsContext &context_;
+  const bool saveUseHexadecimalEscapeSequences_;
   // Buffer to use with raw_string_ostream
   std::string usesBuf_;
   std::string useExtraAttrsBuf_;
diff --git a/flang/lib/Semantics/mod-file.cpp b/flang/lib/Semantics/mod-file.cpp
--- a/flang/lib/Semantics/mod-file.cpp
+++ b/flang/lib/Semantics/mod-file.cpp
@@ -98,6 +98,17 @@
   }
 };
 
+ModFileWriter::ModFileWriter(SemanticsContext &context)
+    : context_{context}, saveUseHexadecimalEscapeSequences_{
+                             parser::useHexadecimalEscapeSequences} {
+  // this flag affects character literals: force it to be consistent
+  parser::useHexadecimalEscapeSequences = false;
+}
+
+ModFileWriter::~ModFileWriter() {
+  parser::useHexadecimalEscapeSequences = saveUseHexadecimalEscapeSequences_;
+}
+
 bool ModFileWriter::WriteAll() {
   WriteAll(context_.globalScope());
   return !context_.AnyFatalError();