diff --git a/basis/compression/zlib/zlib-docs.factor b/basis/compression/zlib/zlib-docs.factor
index edfcea9026..bfe8c12ccd 100644
--- a/basis/compression/zlib/zlib-docs.factor
+++ b/basis/compression/zlib/zlib-docs.factor
@@ -29,10 +29,10 @@ HELP: compressed-size
 
 HELP: uncompress
 { $values
-    { "obj" { $or compressed byte-array } }
+    { "compressed" compressed }
     { "byte-array" byte-array }
 }
-{ $description "Uncompresses, returning a byte-array of the underlying data." } ;
+{ $description "Uncompresses a compressed object, returning a byte-array of the underlying data." } ;
 
 ARTICLE: "compression.zlib" "Compression (ZLIB)"
 "The " { $vocab-link "compression.zlib" } " vocabulary provides support for ZLIB:"
diff --git a/basis/compression/zlib/zlib.factor b/basis/compression/zlib/zlib.factor
index ab47565b0e..3baf8778e4 100644
--- a/basis/compression/zlib/zlib.factor
+++ b/basis/compression/zlib/zlib.factor
@@ -46,7 +46,7 @@ ERROR: zlib-failed n string ;
 
 GENERIC: uncompress ( obj -- byte-array )
 
-M: compressed uncompress
+M: compressed uncompress ( compressed -- byte-array )
     [
         length>> [ <byte-vector> dup underlying>> ] keep
         ulong <ref>
@@ -63,6 +63,6 @@ M: compressed uncompress
         2drop ulong deref memory>byte-array
     ] with-destructors ;
 
-M: byte-array uncompress
+M: byte-array uncompress ( byte-array -- byte-array )
     [ length 5 [0,b) [ 2^ * ] with map ] keep
     '[ _ (uncompress) ] attempt-all ;