diff --git a/bloom-filter/src/main/scala/bloomfilter/mutable/UnsafeBitArray.scala b/bloom-filter/src/main/scala/bloomfilter/mutable/UnsafeBitArray.scala
index f8cd998..2708801 100644
--- a/bloom-filter/src/main/scala/bloomfilter/mutable/UnsafeBitArray.scala
+++ b/bloom-filter/src/main/scala/bloomfilter/mutable/UnsafeBitArray.scala
@@ -33,6 +33,7 @@ class UnsafeBitArray(val numberOfBits: Long) extends Serializable {
       val thatLong = unsafe.getLong(that.ptr + (index >>> 6) * 8L)
       val longAtIndex = combiner(thisLong, thatLong)
       unsafe.putLong(result.ptr + (index >>> 6) * 8L, longAtIndex)
+      result.bitCount += java.lang.Long.bitCount(longAtIndex)
       index += 64
     }
     result
diff --git a/tests/src/test/scala/tests/bloomfilter/mutable/UnsafeBitArraysSpec.scala b/tests/src/test/scala/tests/bloomfilter/mutable/UnsafeBitArraysSpec.scala
index 863102e..143cd17 100644
--- a/tests/src/test/scala/tests/bloomfilter/mutable/UnsafeBitArraysSpec.scala
+++ b/tests/src/test/scala/tests/bloomfilter/mutable/UnsafeBitArraysSpec.scala
@@ -49,7 +49,8 @@ class UnsafeBitArraysSpec extends Properties("UnsafeBitArray") {
       commonIndices.foreach(x => { array.set(x); thatArray.set(x) })
 
       val sut = array & thatArray
-      val result = commonIndices.forall(sut.get)
+      val result = commonIndices.forall(sut.get) &&
+        commonIndices.size == sut.getBitCount
 
       array.dispose()
       thatArray.dispose()