diff --git a/src/xml/xml_native_writer.cc b/src/xml/xml_native_writer.cc
index df2a1ef7..fbfd2261 100644
--- a/src/xml/xml_native_writer.cc
+++ b/src/xml/xml_native_writer.cc
@@ -640,7 +640,13 @@ void mjXWriter::OneActuator(XMLElement* elem, mjCActuator* pact, mjCDef* def) {
 
   // non-plugins: write actuator parameters
   else {
-    WriteAttrInt(elem, "actdim", pact->actdim, def->actuator.actdim);
+    // special handling of actdim which has default value of -1
+    if (writingdefaults) {
+      WriteAttrInt(elem, "actdim", pact->actdim, def->actuator.actdim);
+    } else {
+      int default_actdim = pact->dyntype == mjDYN_NONE ? 0 : 1;
+      WriteAttrInt(elem, "actdim", pact->actdim, default_actdim);
+    }
     WriteAttrKey(elem, "dyntype", dyn_map, dyn_sz, pact->dyntype, def->actuator.dyntype);
     WriteAttrKey(elem, "gaintype", gain_map, gain_sz, pact->gaintype, def->actuator.gaintype);
     WriteAttrKey(elem, "biastype", bias_map, bias_sz, pact->biastype, def->actuator.biastype);
diff --git a/test/xml/xml_native_writer_test.cc b/test/xml/xml_native_writer_test.cc
index 6c9d6470..1527b201 100644
--- a/test/xml/xml_native_writer_test.cc
+++ b/test/xml/xml_native_writer_test.cc
@@ -844,6 +844,8 @@ TEST_F(XMLWriterTest, Actdim) {
     </worldbody>
     <actuator>
       <general joint="hinge" dyntype="user" actdim="2"/>
+      <general joint="hinge" dyntype="filter" dynprm="1"/>
+      <motor joint="hinge"/>
     </actuator>
   </mujoco>
   )";
@@ -851,6 +853,8 @@ TEST_F(XMLWriterTest, Actdim) {
   ASSERT_THAT(model, NotNull());
   std::string saved_xml = SaveAndReadXml(model);
   EXPECT_THAT(saved_xml, HasSubstr("actdim=\"2\""));
+  EXPECT_THAT(saved_xml, Not(HasSubstr("actdim=\"1\"")));
+  EXPECT_THAT(saved_xml, Not(HasSubstr("actdim=\"0\"")));
   mj_deleteModel(model);
 }