zlib does not really support windows size of 8 bits:

Reported by eroen

https://github.com/haskell/zlib/issues/11
https://bugs.gentoo.org/show_bug.cgi?id=613532
diff --git a/test/Test.hs b/test/Test.hs
index bbd8b94..81bd260 100644
--- a/test/Test.hs
+++ b/test/Test.hs
@@ -66,2 +66,3 @@ prop_decompress_after_compress w cp dp =
    -- of the zlib source code.
+   compressWindowBits cp /= WindowBits 8 &&
    (decompressWindowBits dp > compressWindowBits cp || decompressWindowBits dp > WindowBits 8) &&
@@ -76,2 +77,3 @@ prop_gziporzlib1 cp dp =
    decompressWindowBits dp > compressWindowBits cp &&
+   compressWindowBits cp /= WindowBits 8 &&
    decompressBufferSize dp > 0 && compressBufferSize cp > 0 ==>
@@ -85,2 +87,3 @@ prop_gziporzlib2 cp dp =
    decompressWindowBits dp >= compressWindowBits cp &&
+   compressWindowBits cp /= WindowBits 8 &&
    decompressBufferSize dp > 0 && compressBufferSize cp > 0 ==>
@@ -94,2 +97,3 @@ prop_gzip_concat cp dp input =
    decompressWindowBits dp >= compressWindowBits cp &&
+   compressWindowBits cp /= WindowBits 8 &&
    decompressBufferSize dp > 0 && compressBufferSize cp > 0 ==>