diff --git a/win32/build/config.w32 b/win32/build/config.w32
index d5ce9bfc702..3c2ff7a0a9b 100644
--- a/win32/build/config.w32
+++ b/win32/build/config.w32
@@ -139,7 +139,7 @@ ADD_SOURCES("Zend", "zend_language_parser.c zend_language_scanner.c \
 	zend_object_handlers.c zend_objects_API.c \
 	zend_default_classes.c zend_execute.c zend_strtod.c zend_gc.c zend_closures.c \
 	zend_float.c zend_string.c zend_generators.c zend_virtual_cwd.c zend_ast.c \
-	zend_inheritance.c");
+	zend_inheritance.c zend_smart_str.c");
 
 ADD_FLAG("CFLAGS_BD_ZEND", "/D ZEND_ENABLE_STATIC_TSRMLS_CACHE=1");