diff --git a/src/Psalm/Internal/Codebase/Reflection.php b/src/Psalm/Internal/Codebase/Reflection.php
index fc30c134c..7e244f545 100644
--- a/src/Psalm/Internal/Codebase/Reflection.php
+++ b/src/Psalm/Internal/Codebase/Reflection.php
@@ -243,6 +243,7 @@ class Reflection
 
         $storage->is_static = $method->isStatic();
         $storage->abstract = $method->isAbstract();
+        $storage->mutation_free = $storage->external_mutation_free = $method_name === '__construct';
 
         $declaring_method_id = $declaring_class->name . '::' . strtolower((string)$method->getName());
 
diff --git a/tests/PureAnnotationTest.php b/tests/PureAnnotationTest.php
index e5f8d8a7a..140593cd2 100644
--- a/tests/PureAnnotationTest.php
+++ b/tests/PureAnnotationTest.php
@@ -155,6 +155,17 @@ class PureAnnotationTest extends TestCase
                         return \array_map(function(string $s) { return $s;}, $arr);
                     }'
             ],
+            'pureBuiltinCall' => [
+                '<?php
+                    final class Date
+                    {
+                        /** @psalm-pure */
+                        public static function timeZone(string $tzString) : DateTimeZone
+                        {
+                            return new \DateTimeZone($tzString);
+                        }
+                    }',
+            ],
         ];
     }