diff --git a/src/user/user_objects.cc b/src/user/user_objects.cc
index 8a27ed76..8d88b6e3 100644
--- a/src/user/user_objects.cc
+++ b/src/user/user_objects.cc
@@ -70,7 +70,7 @@ static void checksize(double* size, mjtGeom type, mjCBase* object, const char* n
   else {
     for (int i=0; i<mjGEOMINFO[type]; i++) {
       if (size[i]<=0) {
-        throw mjCError(object, "size %d must be positive in geom", "", i);
+        throw mjCError(object, "size %d must be positive in geom", nullptr, i);
       }
     }
   }
diff --git a/test/xml/xml_native_reader_test.cc b/test/xml/xml_native_reader_test.cc
index 5658be39..4c387975 100644
--- a/test/xml/xml_native_reader_test.cc
+++ b/test/xml/xml_native_reader_test.cc
@@ -395,6 +395,24 @@ TEST_F(XMLReaderTest, InvalidNumber) {
   EXPECT_THAT(error.data(), HasSubstr("line 5"));
 }
 
+TEST_F(XMLReaderTest, InvalidNumberOfAttributes) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+    <worldbody>
+      <body pos="0 0 .3">
+        <freejoint/>
+        <geom name="ellipsoid" type="ellipsoid" size=".1 .1"/>
+      </body>
+    </worldbody>
+  </mujoco>
+  )";
+  std::array<char, 1024> error;
+  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
+  ASSERT_THAT(model, IsNull());
+  EXPECT_THAT(error.data(), HasSubstr("size 2 must be positive"));
+  EXPECT_THAT(error.data(), HasSubstr("line 6"));
+}
+
 TEST_F(XMLReaderTest, AllowsSpaces) {
   static constexpr char xml[] = R"(
   <mujoco>
