diff --git a/CHANGES.rst b/CHANGES.rst
index 4d70f4da99..f6dc184bb8 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -4,6 +4,8 @@ Changes
 dev (master)
 ------------
 
+* Remove quadratic behavior within ``GzipDecoder.decompress()`` (Issue #1467)
+
 * ... [Short description of non-trivial change.] (Issue #)
 
 
diff --git a/src/urllib3/response.py b/src/urllib3/response.py
index f0cfbb5499..c112690b0a 100644
--- a/src/urllib3/response.py
+++ b/src/urllib3/response.py
@@ -69,9 +69,9 @@ def __getattr__(self, name):
         return getattr(self._obj, name)
 
     def decompress(self, data):
-        ret = b''
+        ret = bytearray()
         if self._state == GzipDecoderState.SWALLOW_DATA or not data:
-            return ret
+            return bytes(ret)
         while True:
             try:
                 ret += self._obj.decompress(data)
@@ -81,11 +81,11 @@ def decompress(self, data):
                 self._state = GzipDecoderState.SWALLOW_DATA
                 if previous_state == GzipDecoderState.OTHER_MEMBERS:
                     # Allow trailing garbage acceptable in other gzip clients
-                    return ret
+                    return bytes(ret)
                 raise
             data = self._obj.unused_data
             if not data:
-                return ret
+                return bytes(ret)
             self._state = GzipDecoderState.OTHER_MEMBERS
             self._obj = zlib.decompressobj(16 + zlib.MAX_WBITS)