diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index 926c867..0829e10 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -116,6 +116,10 @@ strio_memsize(const void *p)
     return sizeof(struct StringIO);
 }
 
+#ifndef RUBY_TYPED_THREAD_SAFE_FREE
+#define RUBY_TYPED_THREAD_SAFE_FREE RUBY_TYPED_FREE_IMMEDIATELY
+#endif
+
 static const rb_data_type_t strio_data_type = {
     "strio",
     {
@@ -123,7 +127,7 @@ static const rb_data_type_t strio_data_type = {
 	strio_free,
 	strio_memsize,
     },
-    0, 0, RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED
+    0, 0, RUBY_TYPED_THREAD_SAFE_FREE | RUBY_TYPED_WB_PROTECTED
 };
 
 #define check_strio(self) ((struct StringIO*)rb_check_typeddata((self), &strio_data_type))