diff --git a/src/Control/Concurrent/BloomFilter/Internal.hs b/src/Control/Concurrent/BloomFilter/Internal.hs
--- a/src/Control/Concurrent/BloomFilter/Internal.hs
+++ b/src/Control/Concurrent/BloomFilter/Internal.hs
@@ -208,11 +208,13 @@
 log2lFromArraySize sz = 
   either throwBloom return $ do
     let dataSzBytes = sz - sIZEOF_METADATA
-        log2lFloat = logBase 2 ((fromIntegral dataSzBytes / fromIntegral sIZEOF_INT) :: Float)
-        log2l = floor log2lFloat
+        (dataSzWds, z) = dataSzBytes `quotRem` sIZEOF_INT
+        isPowerOfTwo n = n .&. (n - 1) == 0 -- when n > 0
+
     unless (dataSzBytes >= sIZEOF_INT) $ Left "Array is not large enough to be a serialized bloom filter"
-    unless (fromIntegral log2l == log2lFloat) $ Left "Array is an unexpected size for a serialized bloom filter"
-    return log2l
+    unless (isPowerOfTwo dataSzWds && z == 0) $ Left "Array is an unexpected size for a serialized bloom filter"
+    return $!
+      countTrailingZeros dataSzWds -- logBase 2, when isPowerOfTwo
   
 
 
diff --git a/tests/Main.hs b/tests/Main.hs
--- a/tests/Main.hs
+++ b/tests/Main.hs
@@ -417,6 +417,16 @@
 
   serializeRoundtripsTest
   serializeGoldenTests
+  issue2Test
+
+-- Issue #2: this triggered a bug from a careless bit of floating point arithmetic:
+issue2Test :: IO ()
+issue2Test = do
+  sipKey <- pure $ (Bloom.SipKey 1 1)
+  bloom <- Bloom.new sipKey 3 26 :: IO (Bloom.BloomFilter String)
+  bloomBS <- Bloom.serialize bloom
+  void $ (Bloom.deserialize sipKey bloomBS :: IO (Bloom.BloomFilter String))
+
 
 -- For validating that we can serialize and deserialize across machines, and
 -- try to handle forwards compatibility (later).
diff --git a/unagi-bloomfilter.cabal b/unagi-bloomfilter.cabal
--- a/unagi-bloomfilter.cabal
+++ b/unagi-bloomfilter.cabal
@@ -1,5 +1,5 @@
 name:                unagi-bloomfilter
-version:             0.1.1.0
+version:             0.1.1.1
 synopsis:            A fast, cache-efficient, concurrent bloom filter
 description:
   This library implements a fast concurrent bloom filter, based on bloom-1 from