2 files changed, 16 insertions, 4 deletions

diff --git a/src/Network/BitTorrent/Exchange/Block.hs b/src/Network/BitTorrent/Exchange/Block.hs
index 0f437381..6e5b960a 100644
--- a/src/Network/BitTorrent/Exchange/Block.hs
+++ b/src/Network/BitTorrent/Exchange/Block.hs
@@ -317,8 +317,9 @@ spans expectedSize = go 0
 
 -- | /O(1)/. A new empty bucket capable to alloof specified size.
 empty :: PieceSize -> Bucket
-empty 0  = error "empty: Bucket size is zero"
-empty sz = Span sz Nil
+empty sz
+  |   sz < 0  = error "empty: Bucket size must be a non-negative value"
+  | otherwise = Span sz Nil
 {-# INLINE empty #-}
 
 insertSpan :: Pos -> BS.ByteString -> ChunkSize -> Bucket -> Bucket
diff --git a/tests/Network/BitTorrent/Exchange/BlockSpec.hs b/tests/Network/BitTorrent/Exchange/BlockSpec.hs
index d0d71906..2dc8e0b8 100644
--- a/tests/Network/BitTorrent/Exchange/BlockSpec.hs
+++ b/tests/Network/BitTorrent/Exchange/BlockSpec.hs
@@ -1,5 +1,6 @@
 module Network.BitTorrent.Exchange.BlockSpec (spec) where
 import Control.Applicative
+import Control.Exception
 import Data.Maybe
 import Test.Hspec
 import Test.QuickCheck
@@ -15,10 +16,20 @@ instance Arbitrary BlockIx where
   arbitrary = BlockIx <$> arbitrary <*> arbitrary <*> arbitrary
 
 instance Arbitrary Bucket where
-  arbitrary = Block.fromList <$> arbitrary <*> arbitrary
+  arbitrary = do
+    s      <- arbitrary `suchThat` (> 0)
+    chunks <- arbitrary
+    return $ Block.fromList s chunks
+
+isSomeException :: SomeException -> Bool
+isSomeException = const True
 
 spec :: Spec
 spec = do
-  describe "bucket" $ do
+  describe "empty" $ do
+    it "should fail on bad size" $ do
+      evaluate (Block.empty (-1)) `shouldThrow` isSomeException
+
+  describe "toPiece" $ do
     it "render to piece when it is full" $ property $ \ bkt ->
       full bkt == isJust (toPiece bkt)
\ No newline at end of file