diff --git a/ext/zlib/zlib.c b/ext/zlib/zlib.c
index 481d74b..187e358 100644
--- a/ext/zlib/zlib.c
+++ b/ext/zlib/zlib.c
@@ -651,6 +651,7 @@ zstream_init(struct zstream *z, const struct zstream_funcs *func)
     z->stream.avail_in = 0;
     z->stream.next_out = Z_NULL;
     z->stream.avail_out = 0;
+    z->stream.state = Z_NULL;
     z->func = func;
 }
 
diff --git a/test/zlib/test_zlib.rb b/test/zlib/test_zlib.rb
index 48b8f17..71159a0 100644
--- a/test/zlib/test_zlib.rb
+++ b/test/zlib/test_zlib.rb
@@ -1524,6 +1524,8 @@ def test_deflate_stream
     end
 
     def test_gzip
+      assert_raise(Zlib::StreamError) { Zlib.gzip("foo", level: 100) }
+
       actual = Zlib.gzip("foo".freeze)
       actual[4, 4] = "\x00\x00\x00\x00" # replace mtime
       actual[9] = "\xff" # replace OS