diff --git a/libgomp/libgomp.h b/libgomp/libgomp.h
index 607f4c2..acf7f8f 100644
--- a/libgomp/libgomp.h
+++ b/libgomp/libgomp.h
@@ -842,6 +842,11 @@ struct target_mem_desc {
    artificial pointer to "omp declare target link" object.  */
 #define REFCOUNT_LINK (~(uintptr_t) 1)
 
+/* Special offset values.  */
+#define OFFSET_INLINED (~(uintptr_t) 0)
+#define OFFSET_POINTER (~(uintptr_t) 1)
+#define OFFSET_STRUCT (~(uintptr_t) 2)
+
 struct splay_tree_key_s {
   /* Address of the host object.  */
   uintptr_t host_start;
diff --git a/libgomp/target.c b/libgomp/target.c
index ab17650..7220ac6 100644
--- a/libgomp/target.c
+++ b/libgomp/target.c
@@ -45,6 +45,8 @@
 #include "plugin-suffix.h"
 #endif
 
+#define FIELD_TGT_EMPTY (~(size_t) 0)
+
 static void gomp_target_init (void);
 
 /* The whole initialization code for offloading plugins is only run one.  */
@@ -206,8 +208,14 @@ goacc_device_copy_async (struct gomp_device_descr *devicep,
     }
 }
 
-/* Infrastructure for coalescing adjacent or nearly adjacent (in device addresses)
-   host to device memory transfers.  */
+/* Infrastructure for coalescing adjacent or nearly adjacent (in device
+   addresses) host to device memory transfers.  */
+
+struct gomp_coalesce_chunk
+{
+  /* The starting and ending point of a coalesced chunk of memory.  */
+  size_t start, end;
+};
 
 struct gomp_coalesce_buf
 {
@@ -215,10 +223,10 @@ struct gomp_coalesce_buf
      it will be copied to the device.  */
   void *buf;
   struct target_mem_desc *tgt;
-  /* Array with offsets, chunks[2 * i] is the starting offset and
-     chunks[2 * i + 1] ending offset relative to tgt->tgt_start device address
+  /* Array with offsets, chunks[i].start is the starting offset and
+     chunks[i].end ending offset relative to tgt->tgt_start device address
      of chunks which are to be copied to buf and later copied to device.  */
-  size_t *chunks;
+  struct gomp_coalesce_chunk *chunks;
   /* Number of chunks in chunks array, or -1 if coalesce buffering should not
      be performed.  */
   long chunk_cnt;
@@ -251,14 +259,14 @@ gomp_coalesce_buf_add (struct gomp_coalesce_buf *cbuf, size_t start, size_t len)
     {
       if (cbuf->chunk_cnt < 0)
 	return;
-      if (start < cbuf->chunks[2 * cbuf->chunk_cnt - 1])
+      if (start < cbuf->chunks[cbuf->chunk_cnt-1].end)
 	{
 	  cbuf->chunk_cnt = -1;
 	  return;
 	}
-      if (start < cbuf->chunks[2 * cbuf->chunk_cnt - 1] + MAX_COALESCE_BUF_GAP)
+      if (start < cbuf->chunks[cbuf->chunk_cnt-1].end + MAX_COALESCE_BUF_GAP)
 	{
-	  cbuf->chunks[2 * cbuf->chunk_cnt - 1] = start + len;
+	  cbuf->chunks[cbuf->chunk_cnt-1].end = start + len;
 	  cbuf->use_cnt++;
 	  return;
 	}
@@ -268,8 +276,8 @@ gomp_coalesce_buf_add (struct gomp_coalesce_buf *cbuf, size_t start, size_t len)
       if (cbuf->use_cnt == 1)
 	cbuf->chunk_cnt--;
     }
-  cbuf->chunks[2 * cbuf->chunk_cnt] = start;
-  cbuf->chunks[2 * cbuf->chunk_cnt + 1] = start + len;
+  cbuf->chunks[cbuf->chunk_cnt].start = start;
+  cbuf->chunks[cbuf->chunk_cnt].end = start + len;
   cbuf->chunk_cnt++;
   cbuf->use_cnt = 1;
 }
@@ -301,20 +309,20 @@ gomp_copy_host2dev (struct gomp_device_descr *devicep,
   if (cbuf)
     {
       uintptr_t doff = (uintptr_t) d - cbuf->tgt->tgt_start;
-      if (doff < cbuf->chunks[2 * cbuf->chunk_cnt - 1])
+      if (doff < cbuf->chunks[cbuf->chunk_cnt-1].end)
 	{
 	  long first = 0;
 	  long last = cbuf->chunk_cnt - 1;
 	  while (first <= last)
 	    {
 	      long middle = (first + last) >> 1;
-	      if (cbuf->chunks[2 * middle + 1] <= doff)
+	      if (cbuf->chunks[middle].end <= doff)
 		first = middle + 1;
-	      else if (cbuf->chunks[2 * middle] <= doff)
+	      else if (cbuf->chunks[middle].start <= doff)
 		{
-		  if (doff + sz > cbuf->chunks[2 * middle + 1])
+		  if (doff + sz > cbuf->chunks[middle].end)
 		    gomp_fatal ("internal libgomp cbuf error");
-		  memcpy ((char *) cbuf->buf + (doff - cbuf->chunks[0]),
+		  memcpy ((char *) cbuf->buf + (doff - cbuf->chunks[0].start),
 			  h, sz);
 		  return;
 		}
@@ -538,17 +546,25 @@ gomp_map_val (struct target_mem_desc *tgt, void **hostaddrs, size_t i)
     return tgt->list[i].key->tgt->tgt_start
 	   + tgt->list[i].key->tgt_offset
 	   + tgt->list[i].offset;
-  if (tgt->list[i].offset == ~(uintptr_t) 0)
-    return (uintptr_t) hostaddrs[i];
-  if (tgt->list[i].offset == ~(uintptr_t) 1)
-    return 0;
-  if (tgt->list[i].offset == ~(uintptr_t) 2)
-    return tgt->list[i + 1].key->tgt->tgt_start
-	   + tgt->list[i + 1].key->tgt_offset
-	   + tgt->list[i + 1].offset
-	   + (uintptr_t) hostaddrs[i]
-	   - (uintptr_t) hostaddrs[i + 1];
-  return tgt->tgt_start + tgt->list[i].offset;
+
+  switch (tgt->list[i].offset)
+    {
+    case OFFSET_INLINED:
+      return (uintptr_t) hostaddrs[i];
+
+    case OFFSET_POINTER:
+      return 0;
+
+    case OFFSET_STRUCT:
+      return tgt->list[i + 1].key->tgt->tgt_start
+	     + tgt->list[i + 1].key->tgt_offset
+	     + tgt->list[i + 1].offset
+	     + (uintptr_t) hostaddrs[i]
+	     - (uintptr_t) hostaddrs[i + 1];
+
+    default:
+      return tgt->tgt_start + tgt->list[i].offset;
+    }
 }
 
 /* Dynamic array related data structures, interfaces with the compiler.  */
@@ -758,8 +774,8 @@ gomp_map_vars_async (struct gomp_device_descr *devicep,
   cbuf.buf = NULL;
   if (mapnum > 1 || pragma_kind == GOMP_MAP_VARS_TARGET)
     {
-      cbuf.chunks
-	= (size_t *) gomp_alloca ((2 * mapnum + 2) * sizeof (size_t));
+      size_t chunk_size = (mapnum + 1) * sizeof (struct gomp_coalesce_chunk);
+      cbuf.chunks = (struct gomp_coalesce_chunk *) gomp_alloca (chunk_size);
       cbuf.chunk_cnt = 0;
     }
   if (pragma_kind == GOMP_MAP_VARS_TARGET)
@@ -769,8 +785,8 @@ gomp_map_vars_async (struct gomp_device_descr *devicep,
       tgt_size = mapnum * sizeof (void *);
       cbuf.chunk_cnt = 1;
       cbuf.use_cnt = 1 + (mapnum > 1);
-      cbuf.chunks[0] = 0;
-      cbuf.chunks[1] = tgt_size;
+      cbuf.chunks[0].start = 0;
+      cbuf.chunks[0].end = tgt_size;
     }
 
   gomp_mutex_lock (&devicep->lock);
@@ -788,7 +804,7 @@ gomp_map_vars_async (struct gomp_device_descr *devicep,
 	  || (kind & typemask) == GOMP_MAP_FIRSTPRIVATE_INT)
 	{
 	  tgt->list[i].key = NULL;
-	  tgt->list[i].offset = ~(uintptr_t) 0;
+	  tgt->list[i].offset = OFFSET_INLINED;
 	  continue;
 	}
       else if ((kind & typemask) == GOMP_MAP_USE_DEVICE_PTR)
@@ -806,7 +822,7 @@ gomp_map_vars_async (struct gomp_device_descr *devicep,
 	    = (void *) (n->tgt->tgt_start + n->tgt_offset
 			+ cur_node.host_start);
 	  tgt->list[i].key = NULL;
-	  tgt->list[i].offset = ~(uintptr_t) 0;
+	  tgt->list[i].offset = OFFSET_INLINED;
 	  continue;
 	}
       else if ((kind & typemask) == GOMP_MAP_STRUCT)
@@ -817,7 +833,7 @@ gomp_map_vars_async (struct gomp_device_descr *devicep,
 	  cur_node.host_end = (uintptr_t) hostaddrs[last]
 			      + sizes[last];
 	  tgt->list[i].key = NULL;
-	  tgt->list[i].offset = ~(uintptr_t) 2;
+	  tgt->list[i].offset = OFFSET_STRUCT;
 	  splay_tree_key n = splay_tree_lookup (mem_map, &cur_node);
 	  if (n == NULL)
 	    {
@@ -850,7 +866,7 @@ gomp_map_vars_async (struct gomp_device_descr *devicep,
       else if ((kind & typemask) == GOMP_MAP_ALWAYS_POINTER)
 	{
 	  tgt->list[i].key = NULL;
-	  tgt->list[i].offset = ~(uintptr_t) 1;
+	  tgt->list[i].offset = OFFSET_POINTER;
 	  has_firstprivate = true;
 	  continue;
 	}
@@ -894,7 +910,7 @@ gomp_map_vars_async (struct gomp_device_descr *devicep,
 	  if (!n)
 	    {
 	      tgt->list[i].key = NULL;
-	      tgt->list[i].offset = ~(uintptr_t) 1;
+	      tgt->list[i].offset = OFFSET_POINTER;
 	      continue;
 	    }
 	}
@@ -1018,7 +1034,7 @@ gomp_map_vars_async (struct gomp_device_descr *devicep,
       if (cbuf.chunk_cnt > 0)
 	{
 	  cbuf.buf
-	    = malloc (cbuf.chunks[2 * cbuf.chunk_cnt - 1] - cbuf.chunks[0]);
+	    = malloc (cbuf.chunks[cbuf.chunk_cnt-1].end - cbuf.chunks[0].start);
 	  if (cbuf.buf)
 	    {
 	      cbuf.tgt = tgt;
@@ -1144,6 +1160,8 @@ gomp_map_vars_async (struct gomp_device_descr *devicep,
 	    else
 	      k->host_end = k->host_start + sizeof (void *);
 	    splay_tree_key n = splay_tree_lookup (mem_map, k);
+	    /* Need to account for the case where a struct field hasn't been
+	       mapped onto the accelerator yet.  */
 	    if (n && n->refcount != REFCOUNT_LINK)
 	      gomp_map_vars_existing (devicep, aq, n, k, &tgt->list[i],
 				      kind & typemask, cbufp);
@@ -1160,12 +1178,12 @@ gomp_map_vars_async (struct gomp_device_descr *devicep,
 		size_t align = (size_t) 1 << (kind >> rshift);
 		tgt->list[i].key = k;
 		k->tgt = tgt;
-		if (field_tgt_clear != ~(size_t) 0)
+		if (field_tgt_clear != FIELD_TGT_EMPTY)
 		  {
 		    k->tgt_offset = k->host_start - field_tgt_base
 				    + field_tgt_offset;
 		    if (i == field_tgt_clear)
-		      field_tgt_clear = ~(size_t) 0;
+		      field_tgt_clear = FIELD_TGT_EMPTY;
 		  }
 		else
 		  {
@@ -1419,9 +1437,10 @@ gomp_map_vars_async (struct gomp_device_descr *devicep,
       long c = 0;
       for (c = 0; c < cbuf.chunk_cnt; ++c)
 	gomp_copy_host2dev (devicep, aq,
-			    (void *) (tgt->tgt_start + cbuf.chunks[2 * c]),
-			    (char *) cbuf.buf + (cbuf.chunks[2 * c] - cbuf.chunks[0]),
-			    cbuf.chunks[2 * c + 1] - cbuf.chunks[2 * c], NULL);
+			    (void *) (tgt->tgt_start + cbuf.chunks[c].start),
+			    (char *) cbuf.buf + (cbuf.chunks[c].start
+						 - cbuf.chunks[0].start),
+			    cbuf.chunks[c].end - cbuf.chunks[c].start, NULL);
       free (cbuf.buf);
     }
 
