diff --git a/configure.in b/configure.in
index efd14b7a25c98ea13b8b7e34e28c860082783416..0ecab905ef0945faa31fe30e7bd1879d35a9ec95 100644
--- a/configure.in
+++ b/configure.in
@@ -149,7 +149,7 @@ AC_CHECK_HEADERS(zlib.h, , AC_MSG_ERROR(Zlib header (zlib.h) not found. Tor requ
 
 dnl These headers are not essential
 
-AC_CHECK_HEADERS(stdint.h sys/types.h inttypes.h sys/param.h sys/wait.h sys/limits.h netinet/in.h arpa/inet.h machine/limits.h syslog.h sys/time.h sys/resource.h pthread.h)
+AC_CHECK_HEADERS(stdint.h sys/types.h inttypes.h sys/param.h sys/wait.h sys/limits.h netinet/in.h arpa/inet.h machine/limits.h syslog.h sys/time.h sys/resource.h pthread.h stddef.h)
 
 AC_CHECK_FUNCS(gettimeofday ftime socketpair uname inet_aton strptime getrlimit setrlimit strlcat strlcpy strtoull getpwnam ftello pthread_create gethostbyname_r getaddrinfo)
 AC_FUNC_FSEEKO
@@ -206,6 +206,10 @@ AC_CACHE_CHECK([whether memset(0) sets pointers to NULL], tor_cv_null_is_zero,
 [AC_RUN_IFELSE([AC_LANG_SOURCE(
 [[#include <stdlib.h>
 #include <string.h>
+#include <stdio.h>
+#ifdef HAVE_STDDEF_H
+#include <stddef.h>
+#endif
 int main () { char *p1,*p2; p1=NULL; memset(&p2,0,sizeof(p2));
 return memcmp(&p1,&p2,sizeof(char*))?1:0; }]])],
        [tor_cv_null_is_zero=yes],