diff --git a/src/user/user_model.cc b/src/user/user_model.cc
index f3223a0f..556b623b 100644
--- a/src/user/user_model.cc
+++ b/src/user/user_model.cc
@@ -182,6 +182,11 @@ mjCModel& mjCModel::operator=(const mjCModel& other) {
     *static_cast<mjCModel_*>(this) = static_cast<const mjCModel_&>(other);
     *static_cast<mjSpec*>(this) = static_cast<const mjSpec&>(other);
 
+    // copy attached specs first so that we can resolve references to them
+    for (const auto* s : other.specs_) {
+      specs_.push_back(mj_copySpec(s));
+    }
+
     // the world copy constructor takes care of copying the tree
     mjCBody* world = new mjCBody(*other.bodies_[0], this);
     bodies_.push_back(world);
@@ -398,9 +403,6 @@ mjCModel& mjCModel::operator+=(const mjCModel& other) {
     }
     CopyList(numerics_, other.numerics_);
     CopyList(texts_, other.texts_);
-    for (const auto* s : other.specs_) {
-      specs_.push_back(mj_copySpec(s));
-    }
   }
   CopyList(flexes_, other.flexes_);
   CopyList(pairs_, other.pairs_);
diff --git a/test/user/user_api_test.cc b/test/user/user_api_test.cc
index b50b703d..5da06dc1 100644
--- a/test/user/user_api_test.cc
+++ b/test/user/user_api_test.cc
@@ -1998,16 +1998,22 @@ TEST_F(MujocoTest, ResizeParentKeyframe) {
 
 TEST_F(MujocoTest, DifferentUnitsAllowed) {
   mjSpec* child = mj_makeSpec();
-  child->compiler.degree = 1;
+  child->compiler.degree = 0;
   mjsBody* body = mjs_addBody(mjs_findBody(child, "world"), 0);
   body->alt.type = mjORIENTATION_EULER;
-  body->alt.euler[0] = 90;
+  body->alt.euler[0] = -mjPI / 2;
+  mjsGeom* geom = mjs_addGeom(body, 0);
+  geom->size[0] = 1;
+  mjsJoint* joint = mjs_addJoint(body, 0);
+  joint->type = mjJNT_HINGE;
+  joint->range[0] = -mjPI / 4;
+  joint->range[1] = mjPI / 4;
 
   mjSpec* parent = mj_makeSpec();
-  parent->compiler.degree = 0;
+  parent->compiler.degree = 1;
   mjsFrame* frame = mjs_addFrame(mjs_findBody(parent, "world"), 0);
   frame->alt.type = mjORIENTATION_EULER;
-  frame->alt.euler[0] = -mjPI / 2;
+  frame->alt.euler[0] = 90;
 
   EXPECT_THAT(mjs_attachBody(frame, body, "child-", ""), NotNull());
   mjModel* model = mj_compile(parent, 0);
@@ -2016,6 +2022,8 @@ TEST_F(MujocoTest, DifferentUnitsAllowed) {
   EXPECT_NEAR(model->body_quat[5], 0, 1e-12);
   EXPECT_NEAR(model->body_quat[6], 0, 1e-12);
   EXPECT_NEAR(model->body_quat[7], 0, 1e-12);
+  EXPECT_NEAR(model->jnt_range[0], -mjPI / 4, 1e-7);
+  EXPECT_NEAR(model->jnt_range[1], mjPI / 4, 1e-7);
 
   mjSpec* copy = mj_copySpec(parent);
   EXPECT_THAT(copy, NotNull());
@@ -2030,6 +2038,8 @@ TEST_F(MujocoTest, DifferentUnitsAllowed) {
   EXPECT_NEAR(copy_model->body_quat[1], 0, 1e-12);
   EXPECT_NEAR(copy_model->body_quat[2], 0, 1e-12);
   EXPECT_NEAR(copy_model->body_quat[3], 0, 1e-12);
+  EXPECT_NEAR(copy_model->jnt_range[0], -mjPI / 4, 1e-7);
+  EXPECT_NEAR(copy_model->jnt_range[1], mjPI / 4, 1e-7);
 
   mj_deleteModel(copy_model);
   mj_deleteSpec(copy);