diff --git a/flang/runtime/connection.h b/flang/runtime/connection.h
--- a/flang/runtime/connection.h
+++ b/flang/runtime/connection.h
@@ -34,6 +34,13 @@
     // Formatted stream files are viewed as having records, at least on input
     return access != Access::Stream || !isUnformatted.value_or(true);
   }
+
+  template <typename CHAR = char> constexpr bool useUTF8() const {
+    // For wide CHARACTER kinds, always use UTF-8 for formatted I/O.
+    // For single-byte CHARACTER, encode characters >= 0x80 with
+    // UTF-8 iff the mode is set.
+    return sizeof(CHAR) > 1 || isUTF8;
+  }
 };
 
 struct ConnectionState : public ConnectionAttributes {
diff --git a/flang/runtime/edit-output.cpp b/flang/runtime/edit-output.cpp
--- a/flang/runtime/edit-output.cpp
+++ b/flang/runtime/edit-output.cpp
@@ -506,7 +506,7 @@
     // Undelimited list-directed output
     ok = ok && list.EmitLeadingSpaceOrAdvance(io, length > 0 ? 1 : 0, true);
     std::size_t put{0};
-    std::size_t oneIfUTF8{connection.isUTF8 ? 1 : length};
+    std::size_t oneIfUTF8{connection.useUTF8<CHAR>() ? 1 : length};
     while (ok && put < length) {
       if (std::size_t chunk{std::min<std::size_t>(
               std::min<std::size_t>(length - put, oneIfUTF8),
diff --git a/flang/runtime/io-stmt.cpp b/flang/runtime/io-stmt.cpp
--- a/flang/runtime/io-stmt.cpp
+++ b/flang/runtime/io-stmt.cpp
@@ -477,7 +477,7 @@
   // Don't allow sign extension
   using UnsignedChar = std::make_unsigned_t<CHAR>;
   const UnsignedChar *data{reinterpret_cast<const UnsignedChar *>(data0)};
-  if (GetConnectionState().isUTF8) {
+  if (GetConnectionState().useUTF8<CHAR>()) {
     char buffer[256];
     std::size_t at{0};
     while (chars-- > 0) {