Index: ext/zlib/zlib.c
===================================================================
--- ext/zlib/zlib.c	(revision 34377)
+++ ext/zlib/zlib.c	(working copy)
@@ -1732,7 +1732,7 @@ do_inflate(struct zstream *z, VALUE src)
 	return;
     }
     StringValue(src);
-    if (RSTRING_LEN(src) > 0) { /* prevent Z_BUF_ERROR */
+    if (RSTRING_LEN(src) > 0 || z->stream.avail_in > 0) { /* prevent Z_BUF_ERROR */
 	zstream_run(z, (Bytef*)RSTRING_PTR(src), RSTRING_LEN(src), Z_SYNC_FLUSH);
     }
 }
@@ -1749,7 +1749,23 @@ do_inflate(struct zstream *z, VALUE src)
  *
  * Raises a Zlib::NeedDict exception if a preset dictionary is needed to
  * decompress.  Set the dictionary by Zlib::Inflate#set_dictionary and then
- * call this method again with an empty string.  (<i>???</i>)
+ * call this method again with an empty string to flush the stream:
+ *
+ *   inflater = Zlib::Inflate.new
+ *
+ *   begin
+ *     out = inflater.inflate compressed
+ *   rescue Zlib::NeedDict
+ *     # ensure the dictionary matches the stream's required dictionary
+ *     raise unless inflater.adler == Zlib.adler32(dictionary)
+ *
+ *     inflater.set_dictionary dictionary
+ *     inflater.inflate ''
+ *   end
+ *
+ *   # ...
+ *
+ *   inflater.close
  *
  * See also Zlib::Inflate.new
  */
Index: test/zlib/test_zlib.rb
===================================================================
--- test/zlib/test_zlib.rb	(revision 34377)
+++ test/zlib/test_zlib.rb	(working copy)
@@ -195,6 +195,29 @@ if defined? Zlib
       z << "foo" # ???
     end
 
+    def test_inflate_dictionary
+      dictionary = "foo"
+
+      deflate = Zlib::Deflate.new
+      deflate.set_dictionary dictionary
+      compressed = deflate.deflate "foofoofoo", Zlib::FINISH
+      deflate.close
+
+      out = nil
+      inflate = Zlib::Inflate.new
+
+      begin
+        out = inflate.inflate compressed
+
+        flunk "Zlib::NeedDict was not raised"
+      rescue Zlib::NeedDict
+        inflate.set_dictionary dictionary
+        out = inflate.inflate ""
+      end
+
+      assert_equal "foofoofoo", out
+    end
+
     def test_sync
       z = Zlib::Deflate.new
       s = z.deflate("foo" * 1000, Zlib::FULL_FLUSH)