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
@@ -223,16 +223,16 @@
     std::size_t elementBytes{descriptor.ElementBytes()};
     SubscriptValue subscripts[maxRank];
     descriptor.GetLowerBounds(subscripts);
+    std::size_t numElements{descriptor.Elements()};
     if (descriptor.IsContiguous()) { // contiguous unformatted I/O
       char &x{ExtractElement<char>(io, descriptor, subscripts)};
-      auto totalBytes{descriptor.SizeInBytes()};
+      auto totalBytes{numElements * elementBytes};
       if constexpr (DIR == Direction::Output) {
         return unf->Emit(&x, totalBytes, elementBytes);
       } else {
         return unf->Receive(&x, totalBytes, elementBytes);
       }
     } else { // non-contiguous unformatted I/O
-      std::size_t numElements{descriptor.Elements()};
       for (std::size_t j{0}; j < numElements; ++j) {
         char &x{ExtractElement<char>(io, descriptor, subscripts)};
         if constexpr (DIR == Direction::Output) {
diff --git a/flang/runtime/descriptor.h b/flang/runtime/descriptor.h
--- a/flang/runtime/descriptor.h
+++ b/flang/runtime/descriptor.h
@@ -255,6 +255,7 @@
     }
   }
 
+  // Returns size in bytes of the descriptor (not the data)
   static constexpr std::size_t SizeInBytes(
       int rank, bool addendum = false, int lengthTypeParameters = 0) {
     std::size_t bytes{sizeof(Descriptor) - sizeof(Dimension)};