diff --git a/Include/patchlevel.h b/Include/patchlevel.h
index 9fc6e97691d..7f62cdb8892 100644
--- a/Include/patchlevel.h
+++ b/Include/patchlevel.h
@@ -2,7 +2,7 @@
 /* Python version identification scheme.
 
    When the major or minor version changes, the VERSION variable in
-   configure.in must also be changed.
+   configure.ac must also be changed.
 
    There is also (independent) API version information in modsupport.h.
 */
diff --git a/Makefile.pre.in b/Makefile.pre.in
index e4470bdb88d..e01cd2745af 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -151,7 +151,7 @@ SRCDIRS= 	@SRCDIRS@
 SUBDIRSTOO=	Include Lib Misc Demo
 
 # Files and directories to be distributed
-CONFIGFILES=	configure configure.in acconfig.h pyconfig.h.in Makefile.pre.in
+CONFIGFILES=	configure configure.ac acconfig.h pyconfig.h.in Makefile.pre.in
 DISTFILES=	README ChangeLog $(CONFIGFILES)
 DISTDIRS=	$(SUBDIRS) $(SUBDIRSTOO) Ext-dummy
 DIST=		$(DISTFILES) $(DISTDIRS)
@@ -1137,7 +1137,7 @@ recheck:
 	$(SHELL) config.status --recheck
 	$(SHELL) config.status
 
-# Rebuild the configure script from configure.in; also rebuild pyconfig.h.in
+# Rebuild the configure script from configure.ac; also rebuild pyconfig.h.in
 autoconf:
 	(cd $(srcdir); autoconf)
 	(cd $(srcdir); autoheader)
diff --git a/Misc/README.OpenBSD b/Misc/README.OpenBSD
index b417ecc76fc..b9e5976babd 100644
--- a/Misc/README.OpenBSD
+++ b/Misc/README.OpenBSD
@@ -29,7 +29,7 @@ script to disable certain options.  Search for a line that looks like:
 
 If your version is not in that list, e.g., 3.9, add the version
 number.  In this case, you would just need to add a 9 after the 8.
-If you modify configure.in, you will need to regenerate configure
+If you modify configure.ac, you will need to regenerate configure
 with autoconf.
 
 If your version is already in the list, this is not a known problem.
diff --git a/PC/pyconfig.h b/PC/pyconfig.h
index 2444c8ab764..ed6c84f7b83 100644
--- a/PC/pyconfig.h
+++ b/PC/pyconfig.h
@@ -344,7 +344,7 @@ Py_NO_ENABLE_SHARED to find out.  Also support MS_NO_COREDLL for b/w compat */
 #	define SIZEOF_FPOS_T 8
 #	define SIZEOF_HKEY 8
 #	define SIZEOF_SIZE_T 8
-/* configure.in defines HAVE_LARGEFILE_SUPPORT iff HAVE_LONG_LONG,
+/* configure.ac defines HAVE_LARGEFILE_SUPPORT iff HAVE_LONG_LONG,
    sizeof(off_t) > sizeof(long), and sizeof(PY_LONG_LONG) >= sizeof(off_t).
    On Win64 the second condition is not true, but if fpos_t replaces off_t
    then this is true. The uses of HAVE_LARGEFILE_SUPPORT imply that Win64
diff --git a/Python/thread.c b/Python/thread.c
index 4a9b4368ac1..797c8d3a217 100644
--- a/Python/thread.c
+++ b/Python/thread.c
@@ -24,7 +24,7 @@
 #include <stdlib.h>
 
 #ifdef __sgi
-#ifndef HAVE_PTHREAD_H /* XXX Need to check in configure.in */
+#ifndef HAVE_PTHREAD_H /* XXX Need to check in configure.ac */
 #undef _POSIX_THREADS
 #endif
 #endif
diff --git a/configure b/configure
index 90ad156601b..e928bf87b2e 100755
--- a/configure
+++ b/configure
@@ -1,5 +1,5 @@
 #! /bin/sh
-# From configure.in Revision.
+# From configure.ac Revision.
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.68 for python 3.1.
 #
@@ -769,8 +769,7 @@ CFLAGS
 LDFLAGS
 LIBS
 CPPFLAGS
-CPP
-CPPFLAGS'
+CPP'
 
 
 # Initialize some variables set by options.
diff --git a/configure.in b/configure.ac
similarity index 100%
rename from configure.in
rename to configure.ac
diff --git a/pyconfig.h.in b/pyconfig.h.in
index 45678235efc..1c1968b0d97 100644
--- a/pyconfig.h.in
+++ b/pyconfig.h.in
@@ -1,4 +1,4 @@
-/* pyconfig.h.in.  Generated from configure.in by autoheader.  */
+/* pyconfig.h.in.  Generated from configure.ac by autoheader.  */
 
 
 #ifndef Py_PYCONFIG_H
@@ -1102,6 +1102,9 @@
 /* This must be defined on some systems to enable large file support. */
 #undef _LARGEFILE_SOURCE
 
+/* This must be defined on AIX systems to enable large file support. */
+#undef _LARGE_FILES
+
 /* Define to 1 if on MINIX. */
 #undef _MINIX