diff --git a/fragment.go b/fragment.go
index 78ef0597f..6a801bc50 100644
--- a/fragment.go
+++ b/fragment.go
@@ -1776,8 +1776,8 @@ func (f *fragment) mergeBlock(id int, data []pairSet) (sets, clears []pairSet, e
 	clears = make([]pairSet, len(data)+1)
 
 	// Limit upper row/column pair.
-	maxRowID := uint64(id+1) * HashBlockSize
-	maxColumnID := uint64(ShardWidth)
+	maxRowID := (uint64(id+1) * HashBlockSize) - 1
+	maxColumnID := uint64(ShardWidth) - 1
 
 	// Create buffered iterator for local block.
 	itrs := make([]*bufIterator, 1, len(data)+1)
@@ -1857,8 +1857,8 @@ func (f *fragment) mergeBlock(id int, data []pairSet) (sets, clears []pairSet, e
 				sets[i].rowIDs = append(sets[i].rowIDs, min.rowID)
 				sets[i].columnIDs = append(sets[i].columnIDs, min.columnID)
 			} else {
-				clears[i].rowIDs = append(sets[i].rowIDs, min.rowID)
-				clears[i].columnIDs = append(sets[i].columnIDs, min.columnID)
+				clears[i].rowIDs = append(clears[i].rowIDs, min.rowID)
+				clears[i].columnIDs = append(clears[i].columnIDs, min.columnID)
 			}
 		}
 	}
diff --git a/holder_test.go b/holder_test.go
index d9d11f3f6..42c010079 100644
--- a/holder_test.go
+++ b/holder_test.go
@@ -490,6 +490,112 @@ func TestHolderSyncer_SyncHolder(t *testing.T) {
 	}
 }
 
+// Ensure holder can sync with a remote holder and respects
+// the row boundaries of the block.
+func TestHolderSyncer_BlockIteratorLimits(t *testing.T) {
+	c := test.MustNewCluster(t, 3)
+	c[0].Config.Cluster.ReplicaN = 3
+	c[0].Config.AntiEntropy.Interval = 0
+	c[1].Config.Cluster.ReplicaN = 3
+	c[1].Config.AntiEntropy.Interval = 0
+	err := c.Start()
+	if err != nil {
+		t.Fatalf("starting cluster: %v", err)
+	}
+	defer c.Close()
+
+	_, err = c[0].API.CreateIndex(context.Background(), "i", pilosa.IndexOptions{})
+	if err != nil {
+		t.Fatalf("creating index i: %v", err)
+	}
+	_, err = c[0].API.CreateField(context.Background(), "i", "f", pilosa.OptFieldTypeSet(pilosa.DefaultCacheType, pilosa.DefaultCacheSize))
+	if err != nil {
+		t.Fatalf("creating field f: %v", err)
+	}
+
+	blockEdge := uint64(pilosa.HashBlockSize)
+
+	hldr0 := &test.Holder{Holder: c[0].Server.Holder()}
+	hldr1 := &test.Holder{Holder: c[1].Server.Holder()}
+	hldr2 := &test.Holder{Holder: c[2].Server.Holder()}
+
+	// Set data on the local holder.
+	hldr0.SetBit("i", "f", blockEdge-1, 10)
+	hldr0.SetBit("i", "f", blockEdge, 20)
+
+	// Set the same data on one of the replicas
+	// so that we have a quorum.
+	hldr1.SetBit("i", "f", blockEdge-1, 10)
+	hldr1.SetBit("i", "f", blockEdge, 20)
+
+	// Leave the third replica empty to force a block merge.
+	//
+
+	err = c[0].Server.SyncData()
+	if err != nil {
+		t.Fatalf("syncing node 0: %v", err)
+	}
+
+	// Verify data is the same on all nodes.
+	for i, hldr := range []*test.Holder{hldr0, hldr1, hldr2} {
+		if a := hldr.Row("i", "f", blockEdge-1).Columns(); !reflect.DeepEqual(a, []uint64{10}) {
+			t.Errorf("unexpected columns(%d/block 0): %+v", i, a)
+		}
+		if a := hldr.Row("i", "f", blockEdge).Columns(); !reflect.DeepEqual(a, []uint64{20}) {
+			t.Errorf("unexpected columns(%d/block 1): %+v", i, a)
+		}
+	}
+}
+
+// Ensure holder correctly handles clears during block sync.
+func TestHolderSyncer_Clears(t *testing.T) {
+	c := test.MustNewCluster(t, 3)
+	c[0].Config.Cluster.ReplicaN = 3
+	c[0].Config.AntiEntropy.Interval = 0
+	c[1].Config.Cluster.ReplicaN = 3
+	c[1].Config.AntiEntropy.Interval = 0
+	err := c.Start()
+	if err != nil {
+		t.Fatalf("starting cluster: %v", err)
+	}
+	defer c.Close()
+
+	_, err = c[0].API.CreateIndex(context.Background(), "i", pilosa.IndexOptions{})
+	if err != nil {
+		t.Fatalf("creating index i: %v", err)
+	}
+	_, err = c[0].API.CreateField(context.Background(), "i", "f", pilosa.OptFieldTypeSet(pilosa.DefaultCacheType, pilosa.DefaultCacheSize))
+	if err != nil {
+		t.Fatalf("creating field f: %v", err)
+	}
+
+	hldr0 := &test.Holder{Holder: c[0].Server.Holder()}
+	hldr1 := &test.Holder{Holder: c[1].Server.Holder()}
+	hldr2 := &test.Holder{Holder: c[2].Server.Holder()}
+
+	// Set data on the local holder that should be cleared
+	// because it's the only instance of this value.
+	hldr0.SetBit("i", "f", 0, 30)
+
+	// Set similar data on the replicas, but
+	// different from what's on local. This should end
+	// up being set on all replicas
+	hldr1.SetBit("i", "f", 0, 20)
+	hldr2.SetBit("i", "f", 0, 20)
+
+	err = c[0].Server.SyncData()
+	if err != nil {
+		t.Fatalf("syncing node 0: %v", err)
+	}
+
+	// Verify data is the same on all nodes.
+	for i, hldr := range []*test.Holder{hldr0, hldr1, hldr2} {
+		if a := hldr.Row("i", "f", 0).Columns(); !reflect.DeepEqual(a, []uint64{20}) {
+			t.Errorf("unexpected columns(%d): %+v", i, a)
+		}
+	}
+}
+
 // Ensure holder can sync time quantum views with a remote holder.
 func TestHolderSyncer_TimeQuantum(t *testing.T) {
 	c := test.MustNewCluster(t, 2)