diff --git a/cartofacade/capi.go b/cartofacade/capi.go
index 65e2eb110..3f260140f 100644
--- a/cartofacade/capi.go
+++ b/cartofacade/capi.go
@@ -259,15 +259,14 @@ func (vc *Carto) getInternalState() ([]byte, error) {
 		return nil, err
 	}
 
+	interalState := bstringToByteSlice(value.internal_state)
+
 	status = C.viam_carto_get_internal_state_response_destroy(&value)
 	if err := toError(status); err != nil {
 		return nil, err
 	}
 
-	if value.internal_state != nil {
-		return bstringToByteSlice(value.internal_state), nil
-	}
-	return nil, errors.New("nil internal state")
+	return interalState, nil
 }
 
 // this function is only used for testing purposes, but needs to be in this file as CGo is not supported in go test files
diff --git a/viam-cartographer/src/carto_facade/carto_facade.cc b/viam-cartographer/src/carto_facade/carto_facade.cc
index f35283bbe..47f9c29bc 100644
--- a/viam-cartographer/src/carto_facade/carto_facade.cc
+++ b/viam-cartographer/src/carto_facade/carto_facade.cc
@@ -605,7 +605,8 @@ void CartoFacade::GetPointCloudMap(viam_carto_get_point_cloud_map_response *r) {
 // https://viam.atlassian.net/browse/RSDK-3878
 void CartoFacade::GetInternalState(viam_carto_get_internal_state_response *r) {
     boost::uuids::uuid uuid = boost::uuids::random_generator()();
-    std::string filename = path_to_internal_state + "/" + "temp_internal_state_" +
+    std::string filename = path_to_internal_state + "/" +
+                           "temp_internal_state_" +
                            boost::uuids::to_string(uuid) + ".pbstream";
     {
         std::lock_guard<std::mutex> lk(map_builder_mutex);
diff --git a/viam-cartographer/src/carto_facade/carto_facade_test.cc b/viam-cartographer/src/carto_facade/carto_facade_test.cc
index bfd05b75a..cd36d6ac3 100644
--- a/viam-cartographer/src/carto_facade/carto_facade_test.cc
+++ b/viam-cartographer/src/carto_facade/carto_facade_test.cc
@@ -616,6 +616,28 @@ BOOST_AUTO_TEST_CASE(CartoFacade_demo) {
                    VIAM_CARTO_POINTCLOUD_MAP_EMPTY);
     }
 
+    // GetInternalState
+    // Every call to AddSensorReading after the first one (for some
+    // unknown reason) should be persisted in the the internal state.
+    int last_internal_state_response_size = 0;
+    {
+        BOOST_TEST(viam_carto_get_internal_state_response_destroy(nullptr) ==
+                   VIAM_CARTO_GET_INTERNAL_STATE_RESPONSE_INVLALID);
+        BOOST_TEST(viam_carto_get_internal_state(nullptr, nullptr) ==
+                   VIAM_CARTO_VC_INVALID);
+        BOOST_TEST(viam_carto_get_internal_state(vc, nullptr) ==
+                   VIAM_CARTO_GET_INTERNAL_STATE_RESPONSE_INVLALID);
+
+        viam_carto_get_internal_state_response isr;
+        BOOST_TEST(viam_carto_get_internal_state(vc, &isr) ==
+                   VIAM_CARTO_SUCCESS);
+        BOOST_TEST(blength(isr.internal_state) >
+                   last_internal_state_response_size);
+        last_internal_state_response_size = blength(isr.internal_state);
+        BOOST_TEST(viam_carto_get_internal_state_response_destroy(&isr) ==
+                   VIAM_CARTO_SUCCESS);
+    }
+
     // GetPosition unchanged from failed AddSensorReading requests
     {
         viam_carto_get_position_response pr;
@@ -678,6 +700,19 @@ BOOST_AUTO_TEST_CASE(CartoFacade_demo) {
                    VIAM_CARTO_POINTCLOUD_MAP_EMPTY);
     }
 
+    {
+        viam_carto_get_internal_state_response isr;
+        BOOST_TEST(viam_carto_get_internal_state(vc, &isr) ==
+                   VIAM_CARTO_SUCCESS);
+        // special case: apparently the first call to AddSensorReading doesn't
+        // change the internal state, but subsequent calls do.
+        BOOST_TEST(blength(isr.internal_state) ==
+                   last_internal_state_response_size);
+        last_internal_state_response_size = blength(isr.internal_state);
+        BOOST_TEST(viam_carto_get_internal_state_response_destroy(&isr) ==
+                   VIAM_CARTO_SUCCESS);
+    }
+
     // second sensor reading
     {
         VLOG(1) << "viam_carto_add_sensor_reading 2";
@@ -725,6 +760,17 @@ BOOST_AUTO_TEST_CASE(CartoFacade_demo) {
                    VIAM_CARTO_SUCCESS);
     }
 
+    {
+        viam_carto_get_internal_state_response isr;
+        BOOST_TEST(viam_carto_get_internal_state(vc, &isr) ==
+                   VIAM_CARTO_SUCCESS);
+        BOOST_TEST(blength(isr.internal_state) >
+                   last_internal_state_response_size);
+        last_internal_state_response_size = blength(isr.internal_state);
+        BOOST_TEST(viam_carto_get_internal_state_response_destroy(&isr) ==
+                   VIAM_CARTO_SUCCESS);
+    }
+
     // third sensor reading
     {
         VLOG(1) << "viam_carto_add_sensor_reading 3";
@@ -754,12 +800,16 @@ BOOST_AUTO_TEST_CASE(CartoFacade_demo) {
                    VIAM_CARTO_SUCCESS);
     }
 
-    // GetInternalState
-    viam_carto_get_internal_state_response isr;
-    BOOST_TEST(viam_carto_get_internal_state(vc, &isr) == VIAM_CARTO_SUCCESS);
-
-    BOOST_TEST(viam_carto_get_internal_state_response_destroy(&isr) ==
-               VIAM_CARTO_SUCCESS);
+    {
+        viam_carto_get_internal_state_response isr;
+        BOOST_TEST(viam_carto_get_internal_state(vc, &isr) ==
+                   VIAM_CARTO_SUCCESS);
+        BOOST_TEST(blength(isr.internal_state) >
+                   last_internal_state_response_size);
+        last_internal_state_response_size = blength(isr.internal_state);
+        BOOST_TEST(viam_carto_get_internal_state_response_destroy(&isr) ==
+                   VIAM_CARTO_SUCCESS);
+    }
 
     // Stop
     BOOST_TEST(viam_carto_stop(vc) == VIAM_CARTO_SUCCESS);