diff --git a/WHATS_NEW b/WHATS_NEW
index 8e8024145..c119f3eb7 100644
--- a/WHATS_NEW
+++ b/WHATS_NEW
@@ -1,5 +1,6 @@
 Version 2.02.117 - 
 ====================================
+  Fix hang by adjusting cluster mirror regionsize, avoiding CPG msg limit.
   Do not crash when --cachepolicy is given without --cachesettings.
   Add NEEDS_FOREIGN_VGS flag to vgimport so --foreign is always supplied.
   Add --foreign to the 6 display and reporting tools and vgcfgbackup.
diff --git a/lib/metadata/lv_manip.c b/lib/metadata/lv_manip.c
index a77142ce2..c9c1145c4 100644
--- a/lib/metadata/lv_manip.c
+++ b/lib/metadata/lv_manip.c
@@ -6854,7 +6854,8 @@ static struct logical_volume *_lv_create_an_lv(struct volume_group *vg,
 
 		lp->region_size = adjusted_mirror_region_size(vg->extent_size,
 							      lp->extents,
-							      lp->region_size, 0);
+							      lp->region_size, 0,
+							      vg_is_clustered(vg));
 	} else if (pool_lv && seg_is_thin_volume(lp)) {
 		if (!lv_is_thin_pool(pool_lv)) {
 			log_error("Logical volume %s is not a thin pool.",
diff --git a/lib/metadata/metadata-exported.h b/lib/metadata/metadata-exported.h
index 2dbaaf06e..758fa536f 100644
--- a/lib/metadata/metadata-exported.h
+++ b/lib/metadata/metadata-exported.h
@@ -1032,8 +1032,12 @@ int cluster_mirror_is_available(struct cmd_context *cmd);
 int is_temporary_mirror_layer(const struct logical_volume *lv);
 struct logical_volume * find_temporary_mirror(const struct logical_volume *lv);
 uint32_t lv_mirror_count(const struct logical_volume *lv);
+
+/* Remove CMIRROR_REGION_COUNT_LIMIT when http://bugzilla.redhat.com/682771 is fixed */
+#define CMIRROR_REGION_COUNT_LIMIT (256*1024 * 8)
 uint32_t adjusted_mirror_region_size(uint32_t extent_size, uint32_t extents,
-				     uint32_t region_size, int internal);
+				     uint32_t region_size, int internal, int clustered);
+
 int remove_mirrors_from_segments(struct logical_volume *lv,
 				 uint32_t new_mirrors, uint64_t status_mask);
 int add_mirrors_to_segments(struct cmd_context *cmd, struct logical_volume *lv,
diff --git a/lib/metadata/mirror.c b/lib/metadata/mirror.c
index edbf7d4cf..3f2fa2f89 100644
--- a/lib/metadata/mirror.c
+++ b/lib/metadata/mirror.c
@@ -159,9 +159,10 @@ struct lv_segment *find_mirror_seg(struct lv_segment *seg)
  * For internal use only log only in verbose mode
  */
 uint32_t adjusted_mirror_region_size(uint32_t extent_size, uint32_t extents,
-				     uint32_t region_size, int internal)
+				     uint32_t region_size, int internal, int clustered)
 {
 	uint64_t region_max;
+	uint64_t region_min, region_min_pow2;
 
 	region_max = (1 << (ffs((int)extents) - 1)) * (uint64_t) (1 << (ffs((int)extent_size) - 1));
 
@@ -175,6 +176,44 @@ uint32_t adjusted_mirror_region_size(uint32_t extent_size, uint32_t extents,
 				    PRIu32 " sectors.", region_size);
 	}
 
+#ifdef CMIRROR_REGION_COUNT_LIMIT
+	if (clustered) {
+		/*
+		 * The CPG code used by cluster mirrors can only handle a
+		 * payload of < 1MB currently.  (This deficiency is tracked by
+		 * http://bugzilla.redhat.com/682771.)  The region size for cluster
+		 * mirrors must be restricted in such a way as to limit the
+		 * size of the bitmap to < 512kB, because there are two bitmaps
+		 * which get sent around during checkpointing while a cluster
+		 * mirror starts up.  Ergo, the number of regions must not
+		 * exceed 512k * 8.  We also need some room for the other
+		 * checkpointing structures as well, so we reduce by another
+		 * factor of two.
+		 *
+		 * This code should be removed when the CPG restriction is
+		 * lifted.
+		 */
+		region_min = extents;
+		region_min *= extent_size;
+		region_min /= CMIRROR_REGION_COUNT_LIMIT;
+		region_min_pow2 = 1;
+		while (region_min_pow2 < region_min)
+			region_min_pow2 *= 2;
+
+		if (region_size < region_min_pow2) {
+			if (internal)
+				log_print_unless_silent("Increasing mirror region size from %"
+							PRIu32 " to %" PRIu32 " sectors.",
+							region_size, region_min_pow2);
+			else
+				log_verbose("Increasing mirror region size from %"
+					    PRIu32 " to %" PRIu32 " sectors.",
+					    region_size, region_min_pow2);
+			region_size = region_min_pow2;
+		}
+	}
+#endif /* CMIRROR_REGION_COUNT_LIMIT */
+
 	return region_size;
 }
 
@@ -1708,7 +1747,8 @@ static int _add_mirrors_that_preserve_segments(struct logical_volume *lv,
 
 	adjusted_region_size = adjusted_mirror_region_size(lv->vg->extent_size,
 							   lv->le_count,
-							   region_size, 1);
+							   region_size, 1,
+							   vg_is_clustered(lv->vg));
 
 	if (!(ah = allocate_extents(lv->vg, NULL, segtype, 1, mirrors, 0, 0,
 				    lv->le_count, allocatable_pvs, alloc, 0,
diff --git a/lib/mirror/mirrored.c b/lib/mirror/mirrored.c
index 7ab11c216..e57e9bb84 100644
--- a/lib/mirror/mirrored.c
+++ b/lib/mirror/mirrored.c
@@ -435,7 +435,8 @@ static int _mirrored_add_target_line(struct dev_manager *dm, struct dm_pool *mem
 	} else
 		region_size = adjusted_mirror_region_size(seg->lv->vg->extent_size,
 							  seg->area_len,
-							  mirr_state->default_region_size, 1);
+							  mirr_state->default_region_size, 1,
+							  vg_is_clustered(seg->lv->vg));
 
 	if (!dm_tree_node_add_mirror_target(node, len))
 		return_0;
diff --git a/tools/lvconvert.c b/tools/lvconvert.c
index 9ec0b0b15..0e6f16237 100644
--- a/tools/lvconvert.c
+++ b/tools/lvconvert.c
@@ -1209,7 +1209,8 @@ static int _lv_update_log_type(struct cmd_context *cmd,
 	if (old_log_count < log_count) {
 		region_size = adjusted_mirror_region_size(lv->vg->extent_size,
 							  lv->le_count,
-							  region_size, 0);
+							  region_size, 0,
+							  vg_is_clustered(lv->vg));
 
 		if (!add_mirror_log(cmd, original_lv, log_count,
 				    region_size, operable_pvs, alloc))
@@ -1425,7 +1426,8 @@ static int _lvconvert_mirrors_aux(struct cmd_context *cmd,
 
 	region_size = adjusted_mirror_region_size(lv->vg->extent_size,
 						  lv->le_count,
-						  lp->region_size, 0);
+						  lp->region_size, 0,
+						  vg_is_clustered(lv->vg));
 
 	if (!operable_pvs)
 		operable_pvs = lp->pvh;
diff --git a/tools/vgchange.c b/tools/vgchange.c
index c03d81425..bf3d97df2 100644
--- a/tools/vgchange.c
+++ b/tools/vgchange.c
@@ -300,6 +300,8 @@ static int _vgchange_clustered(struct cmd_context *cmd,
 			       struct volume_group *vg)
 {
 	int clustered = arg_int_value(cmd, clustered_ARG, 0);
+	struct lv_list *lvl;
+	struct lv_segment *mirror_seg;
 
 	if (clustered && vg_is_clustered(vg)) {
 		if (vg->system_id && *vg->system_id)
@@ -338,6 +340,20 @@ static int _vgchange_clustered(struct cmd_context *cmd,
 			log_error("No volume groups changed.");
 			return 0;
 		}
+#ifdef CMIRROR_REGION_COUNT_LIMIT
+		dm_list_iterate_items(lvl, &vg->lvs) {
+			if (!lv_is_mirror(lvl->lv))
+				continue;
+			mirror_seg = first_seg(lvl->lv);
+			if ((lvl->lv->size / mirror_seg->region_size) >
+			    CMIRROR_REGION_COUNT_LIMIT) {
+				log_error("Unable to convert %s to clustered mode:"
+					  " Mirror region size of %s is too small.",
+					  vg->name, lvl->lv->name);
+				return 0;
+			}
+		}
+#endif
 	}
 
 	if (!vg_set_system_id(vg, clustered ? NULL : cmd->system_id))