diff --git a/include/thingset.h b/include/thingset.h
index f6eae95..67a53f6 100644
--- a/include/thingset.h
+++ b/include/thingset.h
@@ -1365,10 +1365,10 @@ enum thingset_callback_reason
 };
 
 /** Function to be called before/after read/write operations to groups. */
-typedef void (*thingset_group_callback_t)(enum thingset_callback_reason cb_reason);
+typedef int (*thingset_group_callback_t)(enum thingset_callback_reason cb_reason);
 
 /** Function to be called before/after read/write operations to records. */
-typedef void (*thingset_records_callback_t)(enum thingset_callback_reason cb_reason, int index);
+typedef int (*thingset_records_callback_t)(enum thingset_callback_reason cb_reason, int index);
 
 /** @cond INTERNAL_HIDDEN */
 
diff --git a/src/thingset_common.c b/src/thingset_common.c
index 30cdc97..8bd089d 100644
--- a/src/thingset_common.c
+++ b/src/thingset_common.c
@@ -346,7 +346,10 @@ int thingset_common_update(struct thingset_context *ts)
     ts->api->deserialize_map_start(ts);
 
     if (ts->endpoint.object->data.group_callback != NULL) {
-        ts->endpoint.object->data.group_callback(THINGSET_CALLBACK_PRE_WRITE);
+        int ret = ts->endpoint.object->data.group_callback(THINGSET_CALLBACK_PRE_WRITE);
+        if (ret < 0) {
+            return ts->api->serialize_response(ts, THINGSET_ERR_BAD_REQUEST, "Callback error %i", ret);
+        }
     }
 
     /* actually write data */
@@ -364,7 +367,10 @@ int thingset_common_update(struct thingset_context *ts)
     }
 
     if (ts->endpoint.object->data.group_callback != NULL) {
-        ts->endpoint.object->data.group_callback(THINGSET_CALLBACK_POST_WRITE);
+        int ret = ts->endpoint.object->data.group_callback(THINGSET_CALLBACK_POST_WRITE);
+        if (ret < 0) {
+            return ts->api->serialize_response(ts, THINGSET_ERR_BAD_REQUEST, "Callback error %i", ret);
+        }
     }
 
     /*