diff --git a/src/gen_stub.php b/src/gen_stub.php
index 5b65c0c5..9dcce8fb 100755
--- a/src/gen_stub.php
+++ b/src/gen_stub.php
@@ -834,7 +834,10 @@ class ArgInfo {
 
     private function getDefaultValueAsArginfoString(): string {
         if ($this->hasProperDefaultValue()) {
-            return '"' . addslashes($this->defaultValue) . '"';
+            // The default value is a PHP expression embedded in a C string.
+            // Escape for the outer C layer only; addslashes() leaves line
+            // breaks and other control bytes untouched, producing invalid C++.
+            return '"' . getTranslator()->escapeString($this->defaultValue) . '"';
         }
 
         return "NULL";
@@ -2485,7 +2488,9 @@ class EvaluatedValue
                 if ($forStringDef === '') {
                     $forStringDef = "{$zvalName}_str";
                 }
-                $code .= "\tzend_string *$forStringDef = zend_string_init($cExpr, strlen($cExpr), 1);\n";
+                // getCExpr() emits a C string literal here. sizeof() preserves
+                // embedded NUL bytes, unlike strlen().
+                $code .= "\tzend_string *$forStringDef = zend_string_init($cExpr, sizeof($cExpr) - 1, 1);\n";
                 $code .= "\tZVAL_STR(&$zvalName, $forStringDef);\n";
             }
         } elseif ($this->type->isArray()) {
@@ -2515,14 +2520,12 @@ 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_)) {
-                // 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));
+
+            // ConstExprEvaluator has already decoded literal syntax and
+            // reduced constant string expressions. Emitting that value avoids
+            // leaking heredoc/nowdoc source syntax into generated C++.
+            return '"' . getTranslator()->escapeString((string) $this->value) . '"';
         } elseif ($this->type->isInt() or $this->type->isFloat()) {
             return strval($this->value);
         } elseif ($this->type->isBool()) {
@@ -5107,6 +5110,10 @@ function parseFunctionLike(
             if ($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_) {
+                // Keep this as a PHP expression. ArgInfo escapes the expression
+                // separately when embedding it in generated C++.
+                $defaultValue = var_export($param->default->value, true);
             } 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..28c5d6a5
--- /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
+    quote " slash \\ nul \0 tab \t ??
+    ABC;
+    const VALUE2 = <<<'DEF'
+    $value ?? "quoted" \n \path
+    DEF;
+}
+
+function main()
+{
+    var_dump(bin2hex(Test::VALUE1), bin2hex(Test::VALUE2));
+}
+?>
+--EXPECT--
+string(60) "71756f7465202220736c617368205c206e756c2000207461622009203f3f"
+string(54) "2476616c7565203f3f202271756f74656422205c6e205c70617468"
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..3dc5192b
--- /dev/null
+++ b/tests/compiler/const/heredoc-nowdoc-const-defaults.phpt
@@ -0,0 +1,51 @@
+--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 $x = <<<'ABC'
+$value ?? "quoted" \n \path
+ABC): string {
+    return $x;
+}
+
+function with_binary_default(string $x = <<<ABC
+A\0B
+ABC): string {
+    return $x;
+}
+
+function main()
+{
+    var_dump(G_HEREDOC, G_NOWDOC);
+    $o = new WithProp();
+    var_dump($o->p);
+    var_dump(bin2hex(with_default()), bin2hex(with_binary_default()));
+
+    $default = (new ReflectionFunction('with_default'))->getParameters()[0]->getDefaultValue();
+    $binaryDefault = (new ReflectionFunction('with_binary_default'))->getParameters()[0]->getDefaultValue();
+    var_dump(bin2hex($default), bin2hex($binaryDefault));
+}
+?>
+--EXPECT--
+string(3) "abc"
+string(3) "def"
+string(3) "xyz"
+string(54) "2476616c7565203f3f202271756f74656422205c6e205c70617468"
+string(6) "410042"
+string(54) "2476616c7565203f3f202271756f74656422205c6e205c70617468"
+string(6) "410042"