diff --git a/Zend/Optimizer/block_pass.c b/Zend/Optimizer/block_pass.c
index 61a69dae51e1a..704a16b3ae668 100644
--- a/Zend/Optimizer/block_pass.c
+++ b/Zend/Optimizer/block_pass.c
@@ -714,6 +714,9 @@ static void zend_optimize_block(zend_basic_block *block, zend_op_array *op_array
 								continue;
 							} else if (src->opcode == ZEND_BOOL ||
 							           src->opcode == ZEND_QM_ASSIGN) {
+								if (src->op1_type == IS_VAR) {
+									break;
+								}
 								VAR_SOURCE(opline->op1) = NULL;
 								COPY_NODE(opline->op1, src->op1);
 								MAKE_NOP(src);
diff --git a/ext/opcache/tests/gh21691.phpt b/ext/opcache/tests/gh21691.phpt
new file mode 100644
index 0000000000000..0956a0d62816a
--- /dev/null
+++ b/ext/opcache/tests/gh21691.phpt
@@ -0,0 +1,36 @@
+--TEST--
+GH-21691 (OPcache CFG optimizer breaks reference returns with JMPZ)
+--INI--
+opcache.enable_cli=1
+--EXTENSIONS--
+opcache
+--FILE--
+<?php
+class Base {
+    protected function &getData(): array {
+        $x = [];
+        return $x;
+    }
+
+    public function process(): array {
+        if ($data = &$this->getData() && !isset($data['key'])) {
+        }
+        return $data;
+    }
+}
+
+class Child extends Base {
+    protected function &getData(): array {
+        static $x = ['value' => 42];
+        return $x;
+    }
+}
+
+$child = new Child();
+var_dump($child->process());
+?>
+--EXPECT--
+array(1) {
+  ["value"]=>
+  int(42)
+}