diff --git a/doc/includes/references.h b/doc/includes/references.h
index 79302849..c89a4363 100644
--- a/doc/includes/references.h
+++ b/doc/includes/references.h
@@ -570,7 +570,9 @@ typedef enum mjtObj_ {            // type of MujoCo object
   mjOBJ_TEXT,                     // text
   mjOBJ_TUPLE,                    // tuple
   mjOBJ_KEY,                      // keyframe
-  mjOBJ_PLUGIN                    // plugin instance
+  mjOBJ_PLUGIN,                   // plugin instance
+
+  mjNOBJECT                       // number of object types
 } mjtObj;
 typedef enum mjtConstraint_ {     // type of constraint
   mjCNSTR_EQUALITY    = 0,        // equality constraint
diff --git a/include/mujoco/mjmodel.h b/include/mujoco/mjmodel.h
index 663e191f..49312dd1 100644
--- a/include/mujoco/mjmodel.h
+++ b/include/mujoco/mjmodel.h
@@ -246,7 +246,9 @@ typedef enum mjtObj_ {            // type of MujoCo object
   mjOBJ_TEXT,                     // text
   mjOBJ_TUPLE,                    // tuple
   mjOBJ_KEY,                      // keyframe
-  mjOBJ_PLUGIN                    // plugin instance
+  mjOBJ_PLUGIN,                   // plugin instance
+
+  mjNOBJECT                       // number of object types
 } mjtObj;
 
 
diff --git a/introspect/enums.py b/introspect/enums.py
index bb039f65..4982cf36 100644
--- a/introspect/enums.py
+++ b/introspect/enums.py
@@ -265,6 +265,7 @@ ENUMS: Mapping[str, EnumDecl] = dict([
              ('mjOBJ_TUPLE', 23),
              ('mjOBJ_KEY', 24),
              ('mjOBJ_PLUGIN', 25),
+             ('mjNOBJECT', 26),
          ]),
      )),
     ('mjtConstraint',
diff --git a/src/engine/engine_io.c b/src/engine/engine_io.c
index 32994e9c..ca55358a 100644
--- a/src/engine/engine_io.c
+++ b/src/engine/engine_io.c
@@ -1858,6 +1858,8 @@ static int numObjects(const mjModel* m, mjtObj objtype) {
     return m->nkey;
   case mjOBJ_PLUGIN:
     return m->nplugin;
+  case mjNOBJECT:
+    return -2;
   }
   return -2;
 }
diff --git a/unity/Runtime/Bindings/MjBindings.cs b/unity/Runtime/Bindings/MjBindings.cs
index a17a2694..91bf8765 100644
--- a/unity/Runtime/Bindings/MjBindings.cs
+++ b/unity/Runtime/Bindings/MjBindings.cs
@@ -301,6 +301,7 @@ public enum mjtObj : int{
   mjOBJ_TUPLE = 23,
   mjOBJ_KEY = 24,
   mjOBJ_PLUGIN = 25,
+  mjNOBJECT = 26,
 }
 public enum mjtConstraint : int{
   mjCNSTR_EQUALITY = 0,