diff --git a/pep-0513.txt b/pep-0513.txt
index 894f5b3f3..b20fe60b6 100644
--- a/pep-0513.txt
+++ b/pep-0513.txt
@@ -244,6 +244,7 @@ This is a rather complex and subtle issue that extends beyond
 the scope of ``manylinux1``; for more discussion see: [9]_, [10]_,
 [11]_.
 
+
 UCS-2 vs UCS-4 builds
 ---------------------
 
@@ -282,10 +283,30 @@ But you should never have a wheel with a name like::
   PKG-VERSION-cp27-none-manylinux1_x86_64.whl
                    ^^^^ BAD! Don't do this!
 
+This wheel claims to be simultaneously compatible with *both* ucs2 and
+ucs4 builds, which is bad.
+
 We note for information that the ``ucs4`` ABI appears to be much more
 widespread among Linux CPython distributors.
 
 
+fpectl builds vs. no fpectl builds
+----------------------------------
+
+All extant versions of CPython can be built either with or without the
+``--with-fpectl`` flag to ``configure``. It turns out that this
+changes the CPython ABI: extensions that are built against a
+no-``fpectl`` CPython are always compatible with yes-``fpectl``
+CPython, but the reverse is not necessarily true. (Symptom: errors at
+import time complaining about ``undefined symbol: PyFPE_jbuf``.) See:
+[16]_.
+
+For maximum compatibility, therefore, the CPython used to build
+manylinux1 wheels must be compiled *without* the ``--with-fpectl``
+flag, and manylinux1 extensions must not reference the symbol
+``PyFPE_jbuf``.
+
+
 Compilation of Compliant Wheels
 ===============================
 
@@ -600,6 +621,8 @@ References
    (https://fedoraproject.org/wiki/Bundled_Software_policy)
 .. [15] Debian Policy Manual -- 4.13: Convenience copies of code
     (https://www.debian.org/doc/debian-policy/ch-source.html#s-embeddedfiles)
+.. [16] numpy bug report:
+   https://github.com/numpy/numpy/issues/8415#issuecomment-269095235
 
 
 Copyright