diff --git a/main/src/test/scala/TagsTest.scala b/main/src/test/scala/TagsTest.scala
index 85be939b2..e4edf131a 100644
--- a/main/src/test/scala/TagsTest.scala
+++ b/main/src/test/scala/TagsTest.scala
@@ -2,27 +2,36 @@ package sbt
 
 import org.scalacheck._
 import Gen.{listOf}
-import Prop.forAll
+import Prop._
 import Tags._
 
 object TagsTest extends Properties("Tags")
 {
+	final case class Size(value: Int)
+
 	def tagMap: Gen[TagMap] = for(ts <- listOf(tagAndFrequency)) yield ts.toMap
 	def tagAndFrequency: Gen[(Tag, Int)] = for(t <- tag; count <- Arbitrary.arbitrary[Int]) yield (t, count)
-	def tag: Gen[Tag] = for(s <- Arbitrary.arbitrary[String]) yield Tag(s)
+	def tag: Gen[Tag] = for(s <- Gen.alphaStr if !s.isEmpty) yield Tag(s)
+	def size: Gen[Size] = for(i <- Arbitrary.arbitrary[Int] if i != Int.MinValue) yield Size(math.abs(i))
+
 	implicit def aTagMap = Arbitrary(tagMap)
 	implicit def aTagAndFrequency = Arbitrary(tagAndFrequency)
 	implicit def aTag = Arbitrary(tag)
+	implicit def aSize = Arbitrary(size)
 
 	property("exclusive allows all groups without the exclusive tag") = forAll { (tm: TagMap, tag: Tag) =>
 		excl(tag)(tm - tag)
 	}
-	property("exclusive only allows a group with an excusive tag when the size is one") = forAll { (tm: TagMap, size: Int, etag: Tag) =>
-		val tm2: TagMap = tm.updated(etag, math.abs(size))
-		excl(etag)(tm2) == (size <= 1)
+
+	property("exclusive only allows a group with an excusive tag when the size is one") = forAll { (tm: TagMap, size: Size, etag: Tag) =>
+		val absSize = size.value
+		val tm2: TagMap = tm.updated(etag, absSize).updated(Tags.All, tm.getOrElse(Tags.All, 0) + absSize)
+		(s"TagMap: $tm2") |:
+		( excl(etag)(tm2) == (absSize <= 1) )
 	}
+
 	property("exclusive always allows a group of size one") = forAll { (etag: Tag, mapTag: Tag) =>
-		val tm: TagMap = Map(mapTag -> 1)
+		val tm: TagMap = Map(mapTag -> 1, Tags.All -> 1)
 		excl(etag)(tm)
 	}