diff --git a/source/performance.txt b/source/performance.txt
index ce2e64d001f08210776f4c3b3575baf2f7e7f698_c291cmNlL3BlcmZvcm1hbmNlLnR4dA==..5c47f7c99eeae6e0da0cf0812997453821430a0c_c291cmNlL3BlcmZvcm1hbmNlLnR4dA== 100644
--- a/source/performance.txt
+++ b/source/performance.txt
@@ -64,8 +64,9 @@
 
 * **Missing RPython modules**: A few modules of the standard library
   (like ``csv`` and ``cPickle``) are in C in CPython, but in pure Python
-  in PyPy.  Sometimes the JIT is able to do a relatively good job, and
-  sometimes not.
+  in PyPy.  Sometimes the JIT is able to do a good job on them, and
+  sometimes not.  So it is generally still slower in PyPy than in CPython,
+  but not always (``heapq``, ``json``).
 
 We generally consider things that are slower on PyPy than CPython to be bugs
 of PyPy.  If you find some issue that is not documented here,