Index: flang/runtime/io-stmt.cpp
===================================================================
--- flang/runtime/io-stmt.cpp
+++ flang/runtime/io-stmt.cpp
@@ -915,7 +915,7 @@
       auto pos{unit().position()};
       if (pos == size.value_or(pos + 1)) {
         str = "APPEND";
-      } else if (pos == 0) {
+      } else if (pos == 0 && unit().mayPosition()) {
         str = "REWIND";
       } else {
         str = "ASIS"; // processor-dependent & no common behavior
Index: flang/runtime/unit.cpp
===================================================================
--- flang/runtime/unit.cpp
+++ flang/runtime/unit.cpp
@@ -215,11 +215,13 @@
   RUNTIME_CHECK(terminator, !wasExtant);
   out.Predefine(1);
   out.SetDirection(Direction::Output, handler);
+  out.isUnformatted = false;
   defaultOutput = &out;
   ExternalFileUnit &in{newUnitMap->LookUpOrCreate(5, terminator, wasExtant)};
   RUNTIME_CHECK(terminator, !wasExtant);
   in.Predefine(0);
   in.SetDirection(Direction::Input, handler);
+  in.isUnformatted = false;
   defaultInput = ∈
   // TODO: Set UTF-8 mode from the environment
   unitMap = newUnitMap;