diff --git a/Misc/NEWS.d/next/Library/2020-04-07-05-09-34.bpo-40212.oPYeBs.rst b/Misc/NEWS.d/next/Library/2020-04-07-05-09-34.bpo-40212.oPYeBs.rst
new file mode 100644
index 00000000000000..2e9c3d81180e6a
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-04-07-05-09-34.bpo-40212.oPYeBs.rst
@@ -0,0 +1 @@
+Re-enable :func:`os.posix_fallocate` and :func:`os.posix_fadvise` on AIX.
diff --git a/Modules/clinic/posixmodule.c.h b/Modules/clinic/posixmodule.c.h
index 03c0f221ba98b3..c4f498d233164c 100644
--- a/Modules/clinic/posixmodule.c.h
+++ b/Modules/clinic/posixmodule.c.h
@@ -9418,7 +9418,7 @@ os_truncate(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject
 
 #endif /* (defined HAVE_TRUNCATE || defined MS_WINDOWS) */
 
-#if (defined(HAVE_POSIX_FALLOCATE) && !defined(POSIX_FADVISE_AIX_BUG) && !defined(__wasi__))
+#if (defined(HAVE_POSIX_FALLOCATE) && !defined(__wasi__))
 
 PyDoc_STRVAR(os_posix_fallocate__doc__,
 "posix_fallocate($module, fd, offset, length, /)\n"
@@ -9463,9 +9463,9 @@ os_posix_fallocate(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
     return return_value;
 }
 
-#endif /* (defined(HAVE_POSIX_FALLOCATE) && !defined(POSIX_FADVISE_AIX_BUG) && !defined(__wasi__)) */
+#endif /* (defined(HAVE_POSIX_FALLOCATE) && !defined(__wasi__)) */
 
-#if (defined(HAVE_POSIX_FADVISE) && !defined(POSIX_FADVISE_AIX_BUG))
+#if defined(HAVE_POSIX_FADVISE)
 
 PyDoc_STRVAR(os_posix_fadvise__doc__,
 "posix_fadvise($module, fd, offset, length, advice, /)\n"
@@ -9520,7 +9520,7 @@ os_posix_fadvise(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
     return return_value;
 }
 
-#endif /* (defined(HAVE_POSIX_FADVISE) && !defined(POSIX_FADVISE_AIX_BUG)) */
+#endif /* defined(HAVE_POSIX_FADVISE) */
 
 #if defined(MS_WINDOWS)
 
@@ -13611,4 +13611,4 @@ os__emscripten_log(PyObject *module, PyObject *const *args, Py_ssize_t nargs, Py
 #ifndef OS__EMSCRIPTEN_LOG_METHODDEF
     #define OS__EMSCRIPTEN_LOG_METHODDEF
 #endif /* !defined(OS__EMSCRIPTEN_LOG_METHODDEF) */
-/*[clinic end generated code: output=5fd2aeb6ba9a5df8 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=89c21e2151ac7316 input=a9049054013a1b77]*/
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index ef90ac5de09c65..072027fa0f6174 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -13376,19 +13376,9 @@ os_truncate_impl(PyObject *module, path_t *path, Py_off_t length)
 #endif /* HAVE_TRUNCATE || MS_WINDOWS */
 
 
-/* Issue #22396: On 32-bit AIX platform, the prototypes of os.posix_fadvise()
-   and os.posix_fallocate() in system headers are wrong if _LARGE_FILES is
-   defined, which is the case in Python on AIX. AIX bug report:
-   http://www-01.ibm.com/support/docview.wss?uid=isg1IV56170 */
-#if defined(_AIX) && defined(_LARGE_FILES) && !defined(__64BIT__)
-#  define POSIX_FADVISE_AIX_BUG
-#endif
-
-
 /* GH-111804: Due to posix_fallocate() not having consistent semantics across
    OSs, support was dropped in WASI preview2. */
-#if defined(HAVE_POSIX_FALLOCATE) && !defined(POSIX_FADVISE_AIX_BUG) && \
-    !defined(__wasi__)
+#if defined(HAVE_POSIX_FALLOCATE) && !defined(__wasi__)
 /*[clinic input]
 os.posix_fallocate
 
@@ -13426,10 +13416,10 @@ os_posix_fallocate_impl(PyObject *module, int fd, Py_off_t offset,
     errno = result;
     return posix_error();
 }
-#endif /* HAVE_POSIX_FALLOCATE) && !POSIX_FADVISE_AIX_BUG && !defined(__wasi__) */
+#endif /* HAVE_POSIX_FALLOCATE && !defined(__wasi__) */
 
 
-#if defined(HAVE_POSIX_FADVISE) && !defined(POSIX_FADVISE_AIX_BUG)
+#if defined(HAVE_POSIX_FADVISE)
 /*[clinic input]
 os.posix_fadvise
 
@@ -13473,7 +13463,7 @@ os_posix_fadvise_impl(PyObject *module, int fd, Py_off_t offset,
     errno = result;
     return posix_error();
 }
-#endif /* HAVE_POSIX_FADVISE && !POSIX_FADVISE_AIX_BUG */
+#endif /* HAVE_POSIX_FADVISE */
 
 
 #ifdef MS_WINDOWS