diff --git a/Include/patchlevel.h b/Include/patchlevel.h
index e2478752de6..73508823092 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 a13d1c3649d..31efecacb30 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -160,7 +160,7 @@ SRCDIRS= 	@SRCDIRS@
 SUBDIRSTOO=	Include Lib Misc
 
 # 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)
@@ -1274,7 +1274,7 @@ 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 -Wall)
 	(cd $(srcdir); autoheader -Wall)
diff --git a/PC/pyconfig.h b/PC/pyconfig.h
index 347f1cc3beb..3b71b47ebd2 100644
--- a/PC/pyconfig.h
+++ b/PC/pyconfig.h
@@ -340,7 +340,7 @@ 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/Tools/scripts/patchcheck.py b/Tools/scripts/patchcheck.py
index 0ca712ad31f..503c67a027e 100755
--- a/Tools/scripts/patchcheck.py
+++ b/Tools/scripts/patchcheck.py
@@ -135,7 +135,7 @@ def reported_news(file_paths):
 @status("configure regenerated", modal=True, info=str)
 def regenerated_configure(file_paths):
     """Check if configure has been regenerated."""
-    if 'configure.in' in file_paths:
+    if 'configure.ac' in file_paths:
         return "yes" if 'configure' in file_paths else "no"
     else:
         return "not needed"
@@ -143,7 +143,7 @@ def regenerated_configure(file_paths):
 @status("pyconfig.h.in regenerated", modal=True, info=str)
 def regenerated_pyconfig_h_in(file_paths):
     """Check if pyconfig.h.in has been regenerated."""
-    if 'configure.in' in file_paths:
+    if 'configure.ac' in file_paths:
         return "yes" if 'pyconfig.h.in' in file_paths else "no"
     else:
         return "not needed"
diff --git a/configure b/configure
index 4cb07778d80..7abf15b01b1 100755
--- a/configure
+++ b/configure
@@ -14599,8 +14599,8 @@ esac
 
 cat >>$CONFIG_STATUS <<_ACEOF || ac_write_fail=1
 # Files that config.status was made for.
-config_files="`echo $ac_config_files`"
-config_headers="`echo $ac_config_headers`"
+config_files="$ac_config_files"
+config_headers="$ac_config_headers"
 
 _ACEOF
 
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 efab4fdabd3..0ebcc303937 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