diff --git a/python/mujoco/specs.cc b/python/mujoco/specs.cc
index 219d2565..535e2a2d 100644
--- a/python/mujoco/specs.cc
+++ b/python/mujoco/specs.cc
@@ -465,7 +465,7 @@ PYBIND11_MODULE(_specs, m) {
           throw pybind11::value_error(
               "Only one of frame or site can be specified.");
         }
-        const char* p = prefix.has_value() ? prefix.value().c_str() : "";
+        const char* p = prefix.has_value() ? prefix.value().c_str() : "/";
         const char* s = suffix.has_value() ? suffix.value().c_str() : "";
         raw::MjsElement* attached_frame = nullptr;
         if (frame.has_value()) {
diff --git a/python/mujoco/specs_test.py b/python/mujoco/specs_test.py
index 14ebf262..7a76194a 100644
--- a/python/mujoco/specs_test.py
+++ b/python/mujoco/specs_test.py
@@ -1095,7 +1095,7 @@ class SpecsTest(absltest.TestCase):
     np.testing.assert_array_equal(model2.body_quat[1], [0, 0, 0, 1])
     np.testing.assert_array_equal(model2.body_quat[2], [0, 0, 0, 1])
     self.assertEqual(parent.assets['path/cube.obj'], 'cube_content')
-    self.assertEqual(parent.assets['path/cube2-child2.obj'], 'cube2_content')
+    self.assertEqual(parent.assets['path//cube2-child2.obj'], 'cube2_content')
 
     # Attach another spec to site (referenced by name) and compile again.
     child3 = mujoco.MjSpec()
@@ -1115,7 +1115,7 @@ class SpecsTest(absltest.TestCase):
     np.testing.assert_array_equal(model3.body_quat[2], [0, 0, 0, 1])
     np.testing.assert_array_equal(model3.body_quat[3], [0, 0, 0, 1])
     self.assertEqual(parent.assets['path/cube.obj'], 'cube_content')
-    self.assertEqual(parent.assets['path/cube2-child2.obj'], 'cube2_content')
+    self.assertEqual(parent.assets['path//cube2-child2.obj'], 'cube2_content')
     self.assertEqual(parent.assets['path/child3-cube3.obj'], 'cube3_content')
 
     # Fail to attach to a site that does not exist.
@@ -1176,7 +1176,7 @@ class SpecsTest(absltest.TestCase):
     np.testing.assert_array_equal(model2.body_quat[1], [0, 0, 0, 1])
     np.testing.assert_array_equal(model2.body_quat[2], [0, 0, 0, 1])
     self.assertEqual(parent.assets['path/cube.obj'], 'cube_content')
-    self.assertEqual(parent.assets['path/cube2-child.obj'], 'cube2_content')
+    self.assertEqual(parent.assets['path//cube2-child.obj'], 'cube2_content')
 
     # Attach another spec to frame (referenced by name) and compile again.
     child3 = mujoco.MjSpec()