diff --git a/README.md b/README.md
index acf1f6147..cca5ce9a1 100644
--- a/README.md
+++ b/README.md
@@ -34,7 +34,7 @@ For example, average, moving average, max/min, set
   analytics.
 
 ## Maven
-Current version is `0.1.10`. groupid=`"com.twitter"` artifact=`"algebird-core_2.9.2"`.
+Current version is `0.1.11`. groupid=`"com.twitter"` artifact=`"algebird-core_2.9.2"`.
 
 ## Questions
 > Why not use spire?
diff --git a/algebird-core/src/main/scala/com/twitter/algebird/CountMinSketch.scala b/algebird-core/src/main/scala/com/twitter/algebird/CountMinSketch.scala
index 35d5abe3b..c3299827a 100644
--- a/algebird-core/src/main/scala/com/twitter/algebird/CountMinSketch.scala
+++ b/algebird-core/src/main/scala/com/twitter/algebird/CountMinSketch.scala
@@ -377,6 +377,7 @@ case class CMSHash(a : Int, b : Int, width : Int) extends Function1[Long, Int] {
 /**
  * The 2-dimensional table of counters used in the Count-Min sketch.
  * Each row corresponds to a particular hash function.
+ * TODO: implement a dense matrix type, and use it here
  */
 case class CMSCountsTable(counts : Vector[Vector[Long]]) {
   assert(depth > 0, "Table must have at least 1 row.")
@@ -409,10 +410,14 @@ case class CMSCountsTable(counts : Vector[Vector[Long]]) {
    */
   def ++(other : CMSCountsTable) : CMSCountsTable = {
     assert((depth, width) == (other.depth, other.width), "Tables must have the same dimensions.")
-
-    (0 to (depth - 1)).zip(0 to (width - 1)).foldLeft(this) {
-      case (table, pos) => table + (pos, other.getCount(pos))
+    val iil = Monoid.plus[IndexedSeq[IndexedSeq[Long]]](counts, other.counts)
+    def toVector[V](is: IndexedSeq[V]): Vector[V] = {
+      is match {
+        case v: Vector[V] => v
+        case _ => Vector(is: _*)
+      }
     }
+    CMSCountsTable(toVector(iil.map { toVector(_) }))
   }
 }
 
diff --git a/algebird-test/src/test/scala/com/twitter/algebird/CountMinSketchTest.scala b/algebird-test/src/test/scala/com/twitter/algebird/CountMinSketchTest.scala
index 1c94e758a..01f55d1ff 100644
--- a/algebird-test/src/test/scala/com/twitter/algebird/CountMinSketchTest.scala
+++ b/algebird-test/src/test/scala/com/twitter/algebird/CountMinSketchTest.scala
@@ -97,6 +97,13 @@ class CountMinSketchTest extends Specification {
       cms.frequency(0).estimate must be_==(0)
       cms.frequency(1).estimate must be_==(1)
       cms.frequency(2).estimate must be_==(2)
+
+      val three = CMS_MONOID.create(Seq(1L, 1L, 1L))
+      three.frequency(1L).estimate must be_==(3)
+      val four = CMS_MONOID.create(Seq(1L, 1L, 1L, 1L))
+      four.frequency(1L).estimate must be_==(4)
+      val cms2 = CMS_MONOID.plus(four, three)
+      cms2.frequency(1L).estimate must be_==(7)
     }
 
     "estimate inner products" in {
diff --git a/version.sbt b/version.sbt
index 95c0f0e27..3ec030ef1 100644
--- a/version.sbt
+++ b/version.sbt
@@ -1 +1 @@
-version in ThisBuild := "0.1.10-SNAPSHOT"
+version in ThisBuild := "0.1.12-SNAPSHOT"