diff --git a/ompi/mpi/c/allgather.c b/ompi/mpi/c/allgather.c
index cef55e123d..1ca7b0c49b 100644
--- a/ompi/mpi/c/allgather.c
+++ b/ompi/mpi/c/allgather.c
@@ -14,7 +14,7 @@
  * Copyright (c) 2010      University of Houston.  All rights reserved.
  * Copyright (c) 2013      Los Alamos National Security, LLC. All rights
  *                         reserved.
- * Copyright (c) 2015      Research Organization for Information Science
+ * Copyright (c) 2015-2018 Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
  * $COPYRIGHT$
  *
@@ -64,7 +64,7 @@ int MPI_Allgather(const void *sendbuf, int sendcount, MPI_Datatype sendtype,
         /* check whether the actual send buffer is defined. */
         if (MPI_IN_PLACE == sendbuf) {
             memchecker_call(&opal_memchecker_base_isdefined,
-                            (char *)(recvbuf)+rank*ext,
+                            (char *)(recvbuf)+rank*recvcount*ext,
                             recvcount, recvtype);
         } else {
             memchecker_datatype(sendtype);
diff --git a/ompi/mpi/c/alltoallw.c b/ompi/mpi/c/alltoallw.c
index de354dd992..022cac4231 100644
--- a/ompi/mpi/c/alltoallw.c
+++ b/ompi/mpi/c/alltoallw.c
@@ -53,24 +53,19 @@ int MPI_Alltoallw(const void *sendbuf, const int sendcounts[],
     SPC_RECORD(OMPI_SPC_ALLTOALLW, 1);
 
     MEMCHECKER(
-        ptrdiff_t recv_ext;
-        ptrdiff_t send_ext;
-
         memchecker_comm(comm);
 
         size = OMPI_COMM_IS_INTER(comm)?ompi_comm_remote_size(comm):ompi_comm_size(comm);
         for ( i = 0; i < size; i++ ) {
             if (MPI_IN_PLACE != sendbuf) {
                 memchecker_datatype(sendtypes[i]);
-                ompi_datatype_type_extent(sendtypes[i], &send_ext);
                 memchecker_call(&opal_memchecker_base_isdefined,
-                                (char *)(sendbuf)+sdispls[i]*send_ext,
+                                (char *)(sendbuf)+sdispls[i],
                                 sendcounts[i], sendtypes[i]);
             }
             memchecker_datatype(recvtypes[i]);
-            ompi_datatype_type_extent(recvtypes[i], &recv_ext);
             memchecker_call(&opal_memchecker_base_isaddressable,
-                            (char *)(recvbuf)+rdispls[i]*recv_ext,
+                            (char *)(recvbuf)+rdispls[i],
                             recvcounts[i], recvtypes[i]);
         }
     );
diff --git a/ompi/mpi/c/bcast.c b/ompi/mpi/c/bcast.c
index 7db18f2292..65ecca93cf 100644
--- a/ompi/mpi/c/bcast.c
+++ b/ompi/mpi/c/bcast.c
@@ -9,7 +9,7 @@
  *                         University of Stuttgart.  All rights reserved.
  * Copyright (c) 2004-2005 The Regents of the University of California.
  *                         All rights reserved.
- * Copyright (c) 2015      Research Organization for Information Science
+ * Copyright (c) 2015-2018 Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
  * $COPYRIGHT$
  *
@@ -52,9 +52,10 @@ int MPI_Bcast(void *buffer, int count, MPI_Datatype datatype,
             if (ompi_comm_rank(comm) == root) {
                 /* check whether root's send buffer is defined. */
                 memchecker_call(&opal_memchecker_base_isdefined, buffer, count, datatype);
+            } else {
+                /* check whether receive buffer is addressable. */
+                memchecker_call(&opal_memchecker_base_isaddressable, buffer, count, datatype);
             }
-            /* check whether receive buffer is addressable. */
-            memchecker_call(&opal_memchecker_base_isaddressable, buffer, count, datatype);
         } else {
             if (MPI_ROOT == root) {
                 /* check whether root's send buffer is defined. */
diff --git a/ompi/mpi/c/exscan.c b/ompi/mpi/c/exscan.c
index 45326d94aa..00a26107c1 100644
--- a/ompi/mpi/c/exscan.c
+++ b/ompi/mpi/c/exscan.c
@@ -51,7 +51,14 @@ int MPI_Exscan(const void *sendbuf, void *recvbuf, int count,
 
     MEMCHECKER(
         memchecker_datatype(datatype);
-        memchecker_call(&opal_memchecker_base_isdefined, sendbuf, count, datatype);
+        if (0 != ompi_comm_rank(comm)) {
+            if (MPI_IN_PLACE != sendbuf) {
+                memchecker_call(&opal_memchecker_base_isdefined, sendbuf, count, datatype);
+            } else {
+                memchecker_call(&opal_memchecker_base_isdefined, recvbuf, count, datatype);
+            }
+        }
+        memchecker_call(&opal_memchecker_base_isaddressable, recvbuf, count, datatype);
         memchecker_comm(comm);
     );
 
diff --git a/ompi/mpi/c/iallgather.c b/ompi/mpi/c/iallgather.c
index 8e0abe3fe8..bb7aa504cd 100644
--- a/ompi/mpi/c/iallgather.c
+++ b/ompi/mpi/c/iallgather.c
@@ -14,7 +14,7 @@
  * Copyright (c) 2012      Oak Ridge National Laboratory. All rights reserved.
  * Copyright (c) 2013      Los Alamos National Security, LLC.  All rights
  *                         reserved.
- * Copyright (c) 2015-2019 Research Organization for Information Science
+ * Copyright (c) 2015-2020 Research Organization for Information Science
  *                         and Technology (RIST).  All rights reserved.
  * $COPYRIGHT$
  *
@@ -65,7 +65,7 @@ int MPI_Iallgather(const void *sendbuf, int sendcount, MPI_Datatype sendtype,
         /* check whether the actual send buffer is defined. */
         if (MPI_IN_PLACE == sendbuf) {
             memchecker_call(&opal_memchecker_base_isdefined,
-                            (char *)(recvbuf)+rank*ext,
+                            (char *)(recvbuf)+rank*recvcount*ext,
                             recvcount, recvtype);
         } else {
             memchecker_datatype(sendtype);
diff --git a/ompi/mpi/c/ialltoallw.c b/ompi/mpi/c/ialltoallw.c
index 6dc4af8854..88620d6f11 100644
--- a/ompi/mpi/c/ialltoallw.c
+++ b/ompi/mpi/c/ialltoallw.c
@@ -13,7 +13,7 @@
  * Copyright (c) 2007      Cisco Systems, Inc.  All rights reserved.
  * Copyright (c) 2012-2013 Los Alamos National Security, LLC.  All rights
  *                         reserved.
- * Copyright (c) 2014-2019 Research Organization for Information Science
+ * Copyright (c) 2014-2020 Research Organization for Information Science
  *                         and Technology (RIST).  All rights reserved.
  * $COPYRIGHT$
  *
@@ -54,26 +54,20 @@ int MPI_Ialltoallw(const void *sendbuf, const int sendcounts[], const int sdispl
     SPC_RECORD(OMPI_SPC_IALLTOALLW, 1);
 
     MEMCHECKER(
-        ptrdiff_t recv_ext;
-        ptrdiff_t send_ext;
-
-
         memchecker_comm(comm);
 
         size = OMPI_COMM_IS_INTER(comm)?ompi_comm_remote_size(comm):ompi_comm_size(comm);
         for ( i = 0; i < size; i++ ) {
             if (MPI_IN_PLACE != sendbuf) {
                 memchecker_datatype(sendtypes[i]);
-                ompi_datatype_type_extent(sendtypes[i], &send_ext);
                 memchecker_call(&opal_memchecker_base_isdefined,
-                                (char *)(sendbuf)+sdispls[i]*send_ext,
+                                (char *)(sendbuf)+sdispls[i],
                                 sendcounts[i], sendtypes[i]);
             }
 
             memchecker_datatype(recvtypes[i]);
-            ompi_datatype_type_extent(recvtypes[i], &recv_ext);
             memchecker_call(&opal_memchecker_base_isaddressable,
-                            (char *)(recvbuf)+rdispls[i]*recv_ext,
+                            (char *)(recvbuf)+rdispls[i],
                             recvcounts[i], recvtypes[i]);
         }
     );
diff --git a/ompi/mpi/c/ibcast.c b/ompi/mpi/c/ibcast.c
index 2dcdbb9633..5ab3fb0768 100644
--- a/ompi/mpi/c/ibcast.c
+++ b/ompi/mpi/c/ibcast.c
@@ -1,6 +1,6 @@
 /*
  * Copyright (c) 2012      Oak Rigde National Laboratory. All rights reserved.
- * Copyright (c) 2015-2019 Research Organization for Information Science
+ * Copyright (c) 2015-2020 Research Organization for Information Science
  *                         and Technology (RIST).  All rights reserved.
  * Copyright (c) 2017-2018 The University of Tennessee and The University
  *                         of Tennessee Research Foundation.  All rights
@@ -42,8 +42,24 @@ int MPI_Ibcast(void *buffer, int count, MPI_Datatype datatype,
 
     MEMCHECKER(
         memchecker_datatype(datatype);
-        memchecker_call(&opal_memchecker_base_isdefined, buffer, count, datatype);
         memchecker_comm(comm);
+        if (OMPI_COMM_IS_INTRA(comm)) {
+            if (ompi_comm_rank(comm) == root) {
+                /* check whether root's send buffer is defined. */
+                memchecker_call(&opal_memchecker_base_isdefined, buffer, count, datatype);
+            } else {
+                /* check whether receive buffer is addressable. */
+                memchecker_call(&opal_memchecker_base_isaddressable, buffer, count, datatype);
+            }
+        } else {
+            if (MPI_ROOT == root) {
+                /* check whether root's send buffer is defined. */
+                memchecker_call(&opal_memchecker_base_isdefined, buffer, count, datatype);
+            } else if (MPI_PROC_NULL != root) {
+                /* check whether receive buffer is addressable. */
+                memchecker_call(&opal_memchecker_base_isaddressable, buffer, count, datatype);
+            }
+        }
     );
 
     if (MPI_PARAM_CHECK) {
diff --git a/ompi/mpi/c/iexscan.c b/ompi/mpi/c/iexscan.c
index 4c56e08f1e..8260e5190e 100644
--- a/ompi/mpi/c/iexscan.c
+++ b/ompi/mpi/c/iexscan.c
@@ -52,7 +52,14 @@ int MPI_Iexscan(const void *sendbuf, void *recvbuf, int count,
 
     MEMCHECKER(
         memchecker_datatype(datatype);
-        memchecker_call(&opal_memchecker_base_isdefined, sendbuf, count, datatype);
+        if (0 != ompi_comm_rank(comm)) {
+            if (MPI_IN_PLACE != sendbuf) {
+                memchecker_call(&opal_memchecker_base_isdefined, sendbuf, count, datatype);
+            } else {
+                memchecker_call(&opal_memchecker_base_isdefined, recvbuf, count, datatype);
+            }
+        }
+        memchecker_call(&opal_memchecker_base_isaddressable, recvbuf, count, datatype);
         memchecker_comm(comm);
     );
 
diff --git a/ompi/mpi/c/pack.c b/ompi/mpi/c/pack.c
index 7a8f295a6d..3ce1815578 100644
--- a/ompi/mpi/c/pack.c
+++ b/ompi/mpi/c/pack.c
@@ -13,7 +13,7 @@
  * Copyright (c) 2006      Cisco Systems, Inc.  All rights reserved.
  * Copyright (c) 2013      Los Alamos National Security, LLC.  All rights
  *                         reserved.
- * Copyright (c) 2015-2017 Research Organization for Information Science
+ * Copyright (c) 2015-2018 Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
  * $COPYRIGHT$
  *
@@ -54,6 +54,7 @@ int MPI_Pack(const void *inbuf, int incount, MPI_Datatype datatype,
     MEMCHECKER(
         memchecker_datatype(datatype);
         memchecker_call(&opal_memchecker_base_isdefined, inbuf, incount, datatype);
+        memchecker_call(&opal_memchecker_base_isaddressable, (void *)((char *)outbuf + *position), outsize, MPI_PACKED);
         memchecker_comm(comm);
     );
 
diff --git a/ompi/mpi/c/unpack.c b/ompi/mpi/c/unpack.c
index 0d7e2a68c3..3aaab9d3e7 100644
--- a/ompi/mpi/c/unpack.c
+++ b/ompi/mpi/c/unpack.c
@@ -10,7 +10,7 @@
  * Copyright (c) 2004-2005 The Regents of the University of California.
  *                         All rights reserved.
  * Copyright (c) 2006-2013 Cisco Systems, Inc.  All rights reserved.
- * Copyright (c) 2015-2017 Research Organization for Information Science
+ * Copyright (c) 2015-2018 Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
  * $COPYRIGHT$
  *
@@ -51,7 +51,8 @@ int MPI_Unpack(const void *inbuf, int insize, int *position,
 
     MEMCHECKER(
         memchecker_datatype(datatype);
-        memchecker_call(&opal_memchecker_base_isdefined, outbuf, outcount, datatype);
+        memchecker_call(&opal_memchecker_base_isdefined, inbuf, insize, MPI_PACKED);
+        memchecker_call(&opal_memchecker_base_isaddressable, outbuf, outcount, datatype);
         memchecker_comm(comm);
     );