diff --git a/src/Parser/AssignOpTrait.php b/src/Parser/AssignOpTrait.php
index f15aec98..dc894fb9 100644
--- a/src/Parser/AssignOpTrait.php
+++ b/src/Parser/AssignOpTrait.php
@@ -331,6 +331,12 @@ trait AssignOpTrait
                 // 变量第一次被赋值，确定其类型，由于 PHP 的变量作用域是 function 级的，在 for/while 块中声明的变量，可以在块外使用
                 if (!$this->hasVar($var)) {
                     $finalVarType = $this->getNormalAssignType($type);
+                    // A variable that is later reassigned an incompatible type must be
+                    // declared as a runtime variant (php::Var) up front, otherwise the
+                    // generated C++ would mismatch the scalar declaration.
+                    if (isset($this->variantVars[$var])) {
+                        $finalVarType = Type::VAR;
+                    }
                     $finalVarType = $this->isNativeType($finalVarType) ? $this->getNativeType($finalVarType) : $finalVarType;
                     $this->addLocalVar($var, $finalVarType);
                 } else {