diff --git a/configure.ac b/configure.ac
index f81349bd6..a9360cbec 100644
--- a/configure.ac
+++ b/configure.ac
@@ -271,10 +271,11 @@ AC_CACHE_CHECK([for SYSV IPC],
 #include <sys/types.h>
 #include <sys/ipc.h>
 #include <sys/shm.h>
+#include <sys/stat.h>
 ],[
 { 
     int id;
-    id = shmget(IPC_PRIVATE, 512, SHM_W | SHM_R);
+    id = shmget(IPC_PRIVATE, 512, S_IRUSR | S_IWUSR);
     if (id < 0) return -1;
     return shmctl(id, IPC_RMID, 0);
 }],
@@ -592,7 +593,7 @@ AC_ARG_WITH(khronos-spec-dir, AS_HELP_STRING([--with-khronos-spec-dir=PATH], [Pa
 dnl Extensions.
 AC_ARG_ENABLE(registry,       AS_HELP_STRING([--disable-registry], [Build string registry module (default: enabled)]), [XREGISTRY=$enableval], [XREGISTRY=yes])
 AC_ARG_ENABLE(composite,      AS_HELP_STRING([--disable-composite], [Build Composite extension (default: enabled)]), [COMPOSITE=$enableval], [COMPOSITE=yes])
-AC_ARG_ENABLE(mitshm,         AS_HELP_STRING([--disable-mitshm], [Build SHM extension (default: enabled)]), [MITSHM=$enableval], [MITSHM=yes])
+AC_ARG_ENABLE(mitshm,         AS_HELP_STRING([--disable-mitshm], [Build SHM extension (default: auto)]), [MITSHM=$enableval], [MITSHM=auto])
 AC_ARG_ENABLE(xres,           AS_HELP_STRING([--disable-xres], [Build XRes extension (default: enabled)]), [RES=$enableval], [RES=yes])
 AC_ARG_ENABLE(record,         AS_HELP_STRING([--disable-record], [Build Record extension (default: enabled)]), [RECORD=$enableval], [RECORD=yes])
 AC_ARG_ENABLE(xv,             AS_HELP_STRING([--disable-xv], [Build Xv extension (default: enabled)]), [XV=$enableval], [XV=yes])
@@ -1000,6 +1001,9 @@ if test "x$COMPOSITE" = xyes; then
 	COMPOSITE_INC='-I$(top_srcdir)/composite'
 fi
 
+if test "x$MITSHM" = xauto; then
+	MITSHM="$ac_cv_sysv_ipc"
+fi
 AM_CONDITIONAL(MITSHM, [test "x$MITSHM" = xyes])
 if test "x$MITSHM" = xyes; then
 	AC_DEFINE(MITSHM, 1, [Support MIT-SHM extension])