diff --git a/ext/opcache/config.m4 b/ext/opcache/config.m4
index a388dd787b..6876d37c08 100644
--- a/ext/opcache/config.m4
+++ b/ext/opcache/config.m4
@@ -2,7 +2,7 @@ PHP_ARG_ENABLE([opcache],
   [whether to enable Zend OPcache support],
   [AS_HELP_STRING([--disable-opcache],
     [Disable Zend OPcache support])],
-  [yes])
+  [shared])
 
 PHP_ARG_ENABLE([huge-code-pages],
   [whether to enable copying PHP CODE pages into HUGE PAGES],
@@ -248,6 +248,9 @@ int main() {
 	Optimizer/zend_dump.c,
 	shared,,-DZEND_ENABLE_STATIC_TSRMLS_CACHE=1,,yes)
 
+  PHP_CHECK_LIBRARY(rt, shm_unlink, [PHP_ADD_LIBRARY(rt,1,OPCACHE_SHARED_LIBADD)])
+
   PHP_ADD_BUILD_DIR([$ext_builddir/Optimizer], 1)
   PHP_ADD_EXTENSION_DEP(opcache, pcre)
+  PHP_SUBST(OPCACHE_SHARED_LIBADD)
 fi