diff --git a/ompi/mca/io/romio/romio/include/mpio.h.in b/ompi/mca/io/romio/romio/include/mpio.h.in
index 0e557382d8..b5458d8a75 100644
--- a/ompi/mca/io/romio/romio/include/mpio.h.in
+++ b/ompi/mca/io/romio/romio/include/mpio.h.in
@@ -102,7 +102,11 @@ typedef int MPI_Fint;
 #define MPI_SEEK_CUR            602
 #define MPI_SEEK_END            604
 
+/* Open MPI: don't define MPI_MAX_DATAREP_STRING here; it's defined in          
+   OMPI's mpi.h. */
+#ifndef OPEN_MPI
 #define MPI_MAX_DATAREP_STRING  128
+#endif
 
 #ifndef HAVE_MPI_DARRAY_SUBARRAY
 @HAVE_MPI_DARRAY_SUBARRAY@