diff -r 4b6e6a77e501 Modules/_cryptmodule.c
--- a/Modules/_cryptmodule.c	Sat Oct 22 03:21:55 2016 +0000
+++ b/Modules/_cryptmodule.c	Sat Oct 22 09:40:16 2016 +0200
@@ -5,6 +5,11 @@
 
 #include <sys/types.h>
 
+#ifdef HAVE_CRYPT_H
+#include <crypt.h>
+#endif
+#include <unistd.h>
+
 /* Module crypt */
 
 /*[clinic input]
@@ -36,7 +41,13 @@
 {
     /* On some platforms (AtheOS) crypt returns NULL for an invalid
        salt. Return None in that case. XXX Maybe raise an exception?  */
+#ifdef HAVE_CRYPT_R
+    struct crypt_data data;
+    data.initialized = 0;
+    return Py_BuildValue("s", crypt_r(word, salt, &data));
+#else
     return Py_BuildValue("s", crypt(word, salt));
+#endif
 }
 
 
diff -r 4b6e6a77e501 configure.ac
--- a/configure.ac	Sat Oct 22 03:21:55 2016 +0000
+++ b/configure.ac	Sat Oct 22 09:40:16 2016 +0200
@@ -2033,7 +2033,7 @@
 
 # checks for header files
 AC_HEADER_STDC
-AC_CHECK_HEADERS(asm/types.h conio.h direct.h dlfcn.h errno.h \
+AC_CHECK_HEADERS(asm/types.h conio.h crypt.h direct.h dlfcn.h errno.h \
 fcntl.h grp.h \
 ieeefp.h io.h langinfo.h libintl.h process.h pthread.h \
 sched.h shadow.h signal.h stropts.h termios.h \
@@ -2671,6 +2671,7 @@
 AC_CHECK_LIB(sendfile, sendfile)
 AC_CHECK_LIB(dl, dlopen)	# Dynamic linking for SunOS/Solaris and SYSV
 AC_CHECK_LIB(dld, shl_load)	# Dynamic linking for HP-UX
+AC_CHECK_LIB(crypt, crypt)	# crypt() on Linux
 
 # only check for sem_init if thread support is requested
 if test "$with_threads" = "yes" -o -z "$with_threads"; then
@@ -3403,8 +3404,8 @@
 
 # checks for library functions
 AC_CHECK_FUNCS(alarm accept4 setitimer getitimer bind_textdomain_codeset chown \
- clock confstr ctermid dup3 execv faccessat fchmod fchmodat fchown fchownat \
- fexecve fdopendir fork fpathconf fstatat ftime ftruncate futimesat \
+ clock confstr crypt_r ctermid dup3 execv faccessat fchmod fchmodat fchown \
+ fchownat fexecve fdopendir fork fpathconf fstatat ftime ftruncate futimesat \
  futimens futimes gai_strerror getentropy \
  getgrouplist getgroups getlogin getloadavg getpeername getpgid getpid \
  getpriority getresuid getresgid getpwent getspnam getspent getsid getwd \