diff --git a/flang/runtime/descriptor-io.h b/flang/runtime/descriptor-io.h
--- a/flang/runtime/descriptor-io.h
+++ b/flang/runtime/descriptor-io.h
@@ -279,7 +279,10 @@
         return FormattedRealIO<24, float, DIR>(io, descriptor);
       case 8:
         return FormattedRealIO<53, double, DIR>(io, descriptor);
-#if __x86_64__
+#if _MSC_VER
+        // long double is the same as double with the Microsoft compiler.
+        // Treat as unimplemented.
+#elif __x86_64__
       case 10:
         return FormattedRealIO<64, long double, DIR>(io, descriptor);
 #else
@@ -298,7 +301,10 @@
         return FormattedComplexIO<24, float, DIR>(io, descriptor);
       case 8:
         return FormattedComplexIO<53, double, DIR>(io, descriptor);
-#if __x86_64__
+#if _MSC_VER
+        // long double is the same as double with the Microsoft compiler.
+        // Treat as unimplemented.
+#elif __x86_64__
       case 10:
         return FormattedComplexIO<64, long double, DIR>(io, descriptor);
 #else