diff --git a/CHANGES.md b/CHANGES.md
index 8b51c585..0ff0d517 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -2,6 +2,9 @@
 
 ### Unreleased
 
+* Fix a potential crash in very specific circumstance if GC triggers during a call to `to_json`
+  without first invoking a user defined `#to_json` method.
+
 ### 2025-12-11 (2.18.0)
 
 * Add `:allow_control_characters` parser options, to allow JSON strings containing unescaped ASCII control characters (e.g. newlines).
diff --git a/ext/json/ext/generator/generator.c b/ext/json/ext/generator/generator.c
index dbba99c4..ad925986 100644
--- a/ext/json/ext/generator/generator.c
+++ b/ext/json/ext/generator/generator.c
@@ -1540,7 +1540,9 @@ static VALUE cState_partial_generate(VALUE self, VALUE obj, generator_func func,
         .obj = obj,
         .func = func
     };
-    return rb_ensure(generate_json_try, (VALUE)&data, generate_json_ensure, (VALUE)&data);
+    VALUE result = rb_ensure(generate_json_try, (VALUE)&data, generate_json_ensure, (VALUE)&data);
+    RB_GC_GUARD(self);
+    return result;
 }
 
 /* call-seq: