diff --git a/ompi/datatype/convertor.c b/ompi/datatype/convertor.c
index 98d2df319d..9b2bc5c34f 100644
--- a/ompi/datatype/convertor.c
+++ b/ompi/datatype/convertor.c
@@ -374,7 +374,7 @@ int32_t ompi_convertor_set_position_nocheck( ompi_convertor_t* convertor,
  */
 #define OMPI_CONVERTOR_PREPARE( convertor, datatype, count, pUserBuf )  \
     {                                                                   \
-        convertor->pBaseBuf        = (void*)pUserBuf;                   \
+        convertor->pBaseBuf        = (char*)pUserBuf + datatype->lb;    \
         convertor->count           = count;                             \
                                                                         \
         /* Grab the datatype part of the flags */                       \
diff --git a/ompi/datatype/datatype_internal.h b/ompi/datatype/datatype_internal.h
index 3013e076e2..1662beb624 100644
--- a/ompi/datatype/datatype_internal.h
+++ b/ompi/datatype/datatype_internal.h
@@ -250,19 +250,19 @@ OMPI_DECLSPEC int ompi_ddt_safeguard_pointer_debug_breakpoint( const void* actua
                                                                const ompi_datatype_t* pData,
                                                                int count );
 #define OMPI_DDT_SAFEGUARD_POINTER( ACTPTR, LENGTH, INITPTR, PDATA, COUNT ) \
-{ \
-    char *__lower_bound = (char*)(INITPTR), *__upper_bound; \
-    assert( ((LENGTH) != 0) && ((COUNT) != 0) ); \
-    __lower_bound += (PDATA)->true_lb; \
-    __upper_bound = (INITPTR) + ((PDATA)->ub - (PDATA)->lb) * ((COUNT) - 1) + (PDATA)->true_ub; \
-    if( ((ACTPTR) < __lower_bound) || ((ACTPTR) >= __upper_bound) ) { \
-        ompi_ddt_safeguard_pointer_debug_breakpoint( (ACTPTR), (LENGTH), (INITPTR), (PDATA), (COUNT) ); \
-        opal_output( 0, "%s:%d\n\tPointer %p size %d is outside [%p,%p] for\n\tbase ptr %p count %d and data \n", \
-                     __FILE__, __LINE__, (ACTPTR), (LENGTH), __lower_bound, __upper_bound, \
-                     (INITPTR), (COUNT) ); \
-        ompi_ddt_dump( (PDATA) ); \
-    } \
-}
+    {                                                                   \
+        char *__lower_bound = (char*)(INITPTR), *__upper_bound;         \
+        assert( ((LENGTH) != 0) && ((COUNT) != 0) );                    \
+        __lower_bound += (PDATA)->true_lb - (PDATA)->lb;                \
+        __upper_bound = (INITPTR) + ((PDATA)->ub - (PDATA)->lb) * ((COUNT) - 1) + (PDATA)->true_ub - (PDATA)->lb; \
+        if( ((ACTPTR) < __lower_bound) || ((ACTPTR) >= __upper_bound) ) { \
+            ompi_ddt_safeguard_pointer_debug_breakpoint( (ACTPTR), (LENGTH), (INITPTR), (PDATA), (COUNT) ); \
+            opal_output( 0, "%s:%d\n\tPointer %p size %d is outside [%p,%p] for\n\tbase ptr %p count %d and data \n", \
+                         __FILE__, __LINE__, (ACTPTR), (LENGTH), __lower_bound, __upper_bound, \
+                         (INITPTR), (COUNT) );                          \
+            ompi_ddt_dump( (PDATA) );                                   \
+        }                                                               \
+    }
 
 #else
 #define OMPI_DDT_SAFEGUARD_POINTER( ACTPTR, LENGTH, INITPTR, PDATA, COUNT )
diff --git a/ompi/datatype/datatype_pack.c b/ompi/datatype/datatype_pack.c
index b003e6d2ac..ef5270ef5d 100644
--- a/ompi/datatype/datatype_pack.c
+++ b/ompi/datatype/datatype_pack.c
@@ -762,7 +762,7 @@ ompi_pack_homogeneous_contig_with_gaps_function( ompi_convertor_t* pConv,
                 i++;  /* just to compute the correct source pointer */
                 total_bytes_converted += done;
             }
-            user_memory = pConv->pBaseBuf + pData->true_lb + i * extent;
+            user_memory = pConv->pBaseBuf + i * extent;
             counter = max_allowed / pData->size;
             if( counter > pConv->count ) counter = pConv->count;
             for( i = 0; i < counter; i++ ) {
@@ -827,10 +827,9 @@ ompi_generic_simple_pack_function( ompi_convertor_t* pConvertor,
      * main while loop we will set back the source_base to the correct value. This is
      * due to the fact that the convertor can stop in the middle of a data with a count
      */
-    source_base  = pConvertor->pBaseBuf;
     pStack = pConvertor->pStack + pConvertor->stack_pos;
     pos_desc     = pStack->index;
-    source_base += pStack->disp;
+    source_base  = pConvertor->pBaseBuf + pStack->disp;
     count_desc   = pStack->count;
     pStack--;
     pConvertor->stack_pos--;
diff --git a/ompi/datatype/datatype_unpack.c b/ompi/datatype/datatype_unpack.c
index daec4c2b36..75c929d9c3 100644
--- a/ompi/datatype/datatype_unpack.c
+++ b/ompi/datatype/datatype_unpack.c
@@ -191,7 +191,7 @@ ompi_unpack_homogeneous_contig_function( ompi_convertor_t* pConv,
         if( remaining > (uint32_t)iov[iov_count].iov_len )
             remaining = iov[iov_count].iov_len;
         bConverted = remaining; /* how much will get unpacked this time */
-        user_memory = pConv->pBaseBuf + pData->true_lb;
+        user_memory = pConv->pBaseBuf;
 
         /*opal_output( 0, "unpack_homogeneous_contig( user_memory %p, packed_buffer %p length %d\n",
           user_memory, packed_buffer, remaining );*/
@@ -240,7 +240,7 @@ ompi_unpack_homogeneous_contig_function( ompi_convertor_t* pConv,
                 MEMCPY_CSUM( user_memory, packed_buffer, remaining, pConv );
                 user_memory += remaining;
             }
-            stack->disp = user_memory - pData->true_lb - pConv->pBaseBuf;  /* save the position */
+            stack->disp = user_memory - pConv->pBaseBuf;  /* save the position */
         }
         pConv->bConverted += bConverted;
     }
@@ -332,12 +332,12 @@ ompi_generic_simple_unpack_function( ompi_convertor_t* pConvertor,
      */
     pStack = pConvertor->pStack + pConvertor->stack_pos;
     pos_desc          = pStack->index;
-    user_memory_base += pStack->disp;
+    user_memory_base  = pConvertor->pBaseBuf + pStack->disp;
     count_desc        = pStack->count;
     pStack--;
     pConvertor->stack_pos--;
     pElem = &(description[pos_desc]); 
-    user_memory_base = pConvertor->pBaseBuf + pStack->disp;
+    user_memory_base += pStack->disp;
 
     DO_DEBUG( opal_output( 0, "unpack start pos_desc %d count_desc %d disp %ld\n"
                            "stack_pos %d pos_desc %d count_desc %d disp %ld\n",