diff --git a/tests/017.phpt b/tests/017.phpt
index f63d433..074faec 100644
--- a/tests/017.phpt
+++ b/tests/017.phpt
@@ -1,5 +1,14 @@
 --TEST--
 uopz_redefine
+--SKIPIF--
+<?php
+uopz_allow_exit(true);
+$protect = extension_loaded("Zend OPcache")
+	&& ($conf = opcache_get_configuration()["directives"])
+	&& array_key_exists("opcache.protect_memory", $conf)
+	&&  $conf["opcache.protect_memory"];
+if ($protect) die("xfail known issues with constant redefinition; see #151");
+?>
 --EXTENSIONS--
 uopz
 --INI--
diff --git a/tests/018.phpt b/tests/018.phpt
index 2cb89ac..6715792 100644
--- a/tests/018.phpt
+++ b/tests/018.phpt
@@ -1,5 +1,14 @@
 --TEST--
 uopz_undefine
+--SKIPIF--
+<?php
+uopz_allow_exit(true);
+$protect = extension_loaded("Zend OPcache")
+	&& ($conf = opcache_get_configuration()["directives"])
+	&& array_key_exists("opcache.protect_memory", $conf)
+	&&  $conf["opcache.protect_memory"];
+if ($protect) die("xfail known issues with constant redefinition; see #151");
+?>
 --EXTENSIONS--
 uopz
 --INI--
diff --git a/tests/bugs/0006-uopz-opcache-const-subst.phpt b/tests/bugs/0006-uopz-opcache-const-subst.phpt
index cfd5126..dee386f 100644
--- a/tests/bugs/0006-uopz-opcache-const-subst.phpt
+++ b/tests/bugs/0006-uopz-opcache-const-subst.phpt
@@ -7,6 +7,12 @@ uopz
 	uopz_allow_exit(true);
 	$opcache = ini_get("opcache.enable_cli");
 	if ($opcache === false || $opcache === "0") die("skip opcache required");
+
+    $protect = extension_loaded("Zend OPcache")
+        && ($conf = opcache_get_configuration()["directives"])
+        && array_key_exists("opcache.protect_memory", $conf)
+        &&  $conf["opcache.protect_memory"];
+    if ($protect) die("xfail known issues with constant redefinition; see #151");
 ?>
 --INI--
 uopz.disable=0
diff --git a/tests/bugs/gh53.phpt b/tests/bugs/gh53.phpt
index 5130048..2025977 100644
--- a/tests/bugs/gh53.phpt
+++ b/tests/bugs/gh53.phpt
@@ -2,6 +2,15 @@
 github #53
 --DESCRIPTION--
 uopz_redefine() refuses to redefine a constant as array
+--SKIPIF--
+<?php
+uopz_allow_exit(true);
+$protect = extension_loaded("Zend OPcache")
+	&& ($conf = opcache_get_configuration()["directives"])
+	&& array_key_exists("opcache.protect_memory", $conf)
+	&&  $conf["opcache.protect_memory"];
+if ($protect) die("xfail known issues with constant redefinition; see #151");
+?>
 --EXTENSIONS--
 uopz
 --INI--