diff --git a/ompi/mca/io/romio321/romio/mpi-io/mpioimpl.h b/ompi/mca/io/romio321/romio/mpi-io/mpioimpl.h
index 7c5f0eb394..4eb2843bca 100644
--- a/ompi/mca/io/romio321/romio/mpi-io/mpioimpl.h
+++ b/ompi/mca/io/romio321/romio/mpi-io/mpioimpl.h
@@ -2,6 +2,8 @@
 /* 
  *
  *   Copyright (C) 1997 University of Chicago. 
+ *   Copyright (c) 2018 IBM Corporation. All rights reserved.
+ *   $COPYRIGHT$
  *   See COPYRIGHT notice in top-level directory.
  */
 
@@ -36,7 +38,12 @@
 #define ROMIO_THREAD_CS_ENTER()
 #define ROMIO_THREAD_CS_EXIT()
 #define ROMIO_THREAD_CS_YIELD()
-#define MPIO_DATATYPE_ISCOMMITTED(dtype_, err_) do {} while (0)
+/* The MPI_DATATYPE_ISCOMMITTED macro now always sets err_=0.
+   This is an optimistic approach for Open MPI, but it is likely other
+   upper layers already checked the datatype was committed.
+   Not setting err_ is incorrect since it can lead to use of
+   uninitialized variable.*/
+#define MPIO_DATATYPE_ISCOMMITTED(dtype_, err_) do { err_ = 0; } while (0)
 #ifdef HAVE_WINDOWS_H
 #define MPIU_UNREFERENCED_ARG(a) a
 #else