diff --git a/test/netlib/test_encoding.py b/test/netlib/test_encoding.py
index de10fc486..a5e81379d 100644
--- a/test/netlib/test_encoding.py
+++ b/test/netlib/test_encoding.py
@@ -1,3 +1,4 @@
+import mock
 from netlib import encoding, tutils
 
 
@@ -37,3 +38,32 @@ def test_deflate():
     )
     with tutils.raises(ValueError):
         encoding.decode(b"bogus", "deflate")
+
+
+def test_cache():
+    decode_gzip = mock.MagicMock()
+    decode_gzip.return_value = b"decoded"
+    encode_gzip = mock.MagicMock()
+    encode_gzip.return_value = b"encoded"
+
+    with mock.patch.dict(encoding.custom_decode, gzip=decode_gzip):
+        with mock.patch.dict(encoding.custom_encode, gzip=encode_gzip):
+            assert encoding.decode(b"encoded", "gzip") == b"decoded"
+            assert decode_gzip.call_count == 1
+
+            # should be cached
+            assert encoding.decode(b"encoded", "gzip") == b"decoded"
+            assert decode_gzip.call_count == 1
+
+            # the other way around as well
+            assert encoding.encode(b"decoded", "gzip") == b"encoded"
+            assert encode_gzip.call_count == 0
+
+            # different encoding
+            decode_gzip.return_value = b"bar"
+            assert encoding.encode(b"decoded", "deflate") != b"decoded"
+            assert encode_gzip.call_count == 0
+
+            # This is not in the cache anymore
+            assert encoding.encode(b"decoded", "gzip") == b"encoded"
+            assert encode_gzip.call_count == 1