diff --git a/ext/reflection/php_reflection.c b/ext/reflection/php_reflection.c
index 016851e9e54..f5c2b0f63c0 100644
--- a/ext/reflection/php_reflection.c
+++ b/ext/reflection/php_reflection.c
@@ -557,7 +557,10 @@ static void _class_const_string(smart_str *str, char *name, zend_class_constant
 	char *visibility = zend_visibility_string(Z_ACCESS_FLAGS(c->value));
 	const char *type;
 
-	zval_update_constant_ex(&c->value, c->ce);
+	if (zval_update_constant_ex(&c->value, c->ce) == FAILURE) {
+		return;
+	}
+
 	type = zend_zval_type_name(&c->value);
 
 	if (Z_TYPE(c->value) == IS_ARRAY) {
diff --git a/ext/reflection/tests/ReflectionClassConstant_toString_error.phpt b/ext/reflection/tests/ReflectionClassConstant_toString_error.phpt
new file mode 100644
index 00000000000..54290e97aa3
--- /dev/null
+++ b/ext/reflection/tests/ReflectionClassConstant_toString_error.phpt
@@ -0,0 +1,18 @@
+--TEST--
+Exception thrown while converting ReflectionClassConstant to string
+--FILE--
+<?php
+
+class B {
+    const X = self::UNKNOWN;
+}
+
+try {
+    echo new ReflectionClassConstant('B', 'X');
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+
+?>
+--EXPECT--
+Undefined constant self::UNKNOWN