diff --git a/src/gen_stub.php b/src/gen_stub.php
index 5b65c0c5..ff1406a0 100755
--- a/src/gen_stub.php
+++ b/src/gen_stub.php
@@ -2515,14 +2515,20 @@ class EvaluatedValue
                 return '"' . getTranslator()->escapeString((string) $this->value) . '"';
             } elseif ($this->expr instanceof Expr\ConstFetch) {
                 return getTranslator()->getConstValue($this->expr->name->toString());
-            } elseif (!($this->expr instanceof String_)) {
+            } elseif ($this->expr instanceof String_) {
+                // Heredoc/nowdoc and quoted string literals: emit the decoded
+                // value directly. Pretty-printing a heredoc/nowdoc would leak
+                // the `<<<MARKER ... MARKER` source syntax into the generated
+                // C++, which is invalid; for quoted strings this is also the
+                // correct, simpler form.
+                return '"' . getTranslator()->escapeString((string) $this->value) . '"';
+            } else {
                 // ConstExprEvaluator has already reduced concatenations and
                 // other constant string expressions to their PHP value. Emit
                 // that value as a C string literal instead of rejecting every
                 // non-literal string expression.
                 return '"' . getTranslator()->escapeString((string) $this->value) . '"';
             }
-            $expr = preg_replace("/(^'|'$)/", '"', getTranslator()->escapeString($expr));
         } elseif ($this->type->isInt() or $this->type->isFloat()) {
             return strval($this->value);
         } elseif ($this->type->isBool()) {
@@ -5107,6 +5113,13 @@ function parseFunctionLike(
             if ($param->default instanceof Expr\ClassConstFetch && $param->default->class->toLowerString() === "self") {
                 $defaultValue = getTranslator()->getClassConstValue($func, $name->className->name, $param->default->name->name);
                 $defaultValue = var_export($defaultValue, true);
+            } elseif ($param->default instanceof String_ &&
+                in_array($param->default->getAttribute('kind'), [String_::KIND_HEREDOC, String_::KIND_NOWDOC], true)
+            ) {
+                // heredoc/nowdoc: prettyPrint 会输出 `<<<MARKER ... MARKER` 源码语法，
+                // 在 arginfo 的 C 字符串字面量中属于非法内容；改为输出解码后的字符串值
+                // （PHP 双引号字符串字面量，经 addslashes 包裹后仍可被 arginfo 正确求值）。
+                $defaultValue = '"' . getTranslator()->escapeString((string) $param->default->value) . '"';
             } else {
                 $defaultValue = $param->default ? $prettyPrinter->prettyPrintExpr($param->default) : null;
             }
diff --git a/tests/compiler/const/class-const-heredoc-nowdoc.phpt b/tests/compiler/const/class-const-heredoc-nowdoc.phpt
new file mode 100644
index 00000000..350c1ad7
--- /dev/null
+++ b/tests/compiler/const/class-const-heredoc-nowdoc.phpt
@@ -0,0 +1,23 @@
+--TEST--
+class constants with heredoc and nowdoc syntax
+--FILE--
+<?php
+
+class Test
+{
+    const VALUE1 = <<<ABC
+    abc
+    ABC;
+    const VALUE2 = <<<'DEF'
+    def
+    DEF;
+}
+
+function main()
+{
+    var_dump(Test::VALUE1, Test::VALUE2);
+}
+?>
+--EXPECT--
+string(3) "abc"
+string(3) "def"
diff --git a/tests/compiler/const/heredoc-nowdoc-const-defaults.phpt b/tests/compiler/const/heredoc-nowdoc-const-defaults.phpt
new file mode 100644
index 00000000..07868984
--- /dev/null
+++ b/tests/compiler/const/heredoc-nowdoc-const-defaults.phpt
@@ -0,0 +1,38 @@
+--TEST--
+global constants, property defaults and parameter defaults with heredoc/nowdoc syntax
+--FILE--
+<?php
+
+const G_HEREDOC = <<<ABC
+    abc
+    ABC;
+const G_NOWDOC = <<<'DEF'
+    def
+    DEF;
+
+class WithProp
+{
+    public string $p = <<<ABC
+    xyz
+    ABC;
+}
+
+function with_default(string $x = <<<ABC
+abc
+ABC): string {
+    return $x;
+}
+
+function main()
+{
+    var_dump(G_HEREDOC, G_NOWDOC);
+    $o = new WithProp();
+    var_dump($o->p);
+    var_dump(with_default());
+}
+?>
+--EXPECT--
+string(3) "abc"
+string(3) "def"
+string(3) "xyz"
+string(3) "abc"