Index: flang/docs/Extensions.md
===================================================================
--- flang/docs/Extensions.md
+++ flang/docs/Extensions.md
@@ -585,3 +585,7 @@
 
 * `EXTENDS_TYPE_OF()` returns `.TRUE.` if both of its arguments have the
   same type, a case that is technically implementation-defined.
+
+* `ENCODING=` is not in the list of changeable modes on an I/O unit,
+  but every Fortran compiler allows the encoding to be changed on an
+  open unit.
Index: flang/runtime/io-api.cpp
===================================================================
--- flang/runtime/io-api.cpp
+++ flang/runtime/io-api.cpp
@@ -927,25 +927,20 @@
     io.GetIoErrorHandler().Crash(
         "SetEncoding() called after GetNewUnit() for an OPEN statement");
   }
-  bool isUTF8{false};
+  // Allow the encoding to be changed on an open unit -- it's
+  // useful and safe.
   static const char *keywords[]{"UTF-8", "DEFAULT", nullptr};
   switch (IdentifyValue(keyword, length, keywords)) {
   case 0:
-    isUTF8 = true;
+    open->unit().isUTF8 = true;
     break;
   case 1:
-    isUTF8 = false;
+    open->unit().isUTF8 = false;
     break;
   default:
     open->SignalError(IostatErrorInKeyword, "Invalid ENCODING='%.*s'",
         static_cast<int>(length), keyword);
   }
-  if (isUTF8 != open->unit().isUTF8) {
-    if (open->wasExtant()) {
-      open->SignalError("ENCODING= may not be changed on an open unit");
-    }
-    open->unit().isUTF8 = isUTF8;
-  }
   return true;
 }