diff --git a/core/include/rmutex.h b/core/include/rmutex.h
index 880bbf0ea2..6bf99efd7e 100644
--- a/core/include/rmutex.h
+++ b/core/include/rmutex.h
@@ -7,7 +7,7 @@
  */
 
 /**
- * @ingroup     core_sync Synchronization
+ * @ingroup     core_sync
  * @brief       Recursive Mutex for thread synchronization
  * @{
  *
diff --git a/core/include/thread.h b/core/include/thread.h
index d59cabb2bf..79ca817a17 100644
--- a/core/include/thread.h
+++ b/core/include/thread.h
@@ -241,7 +241,6 @@ struct _thread {
 
 /**
  * @def THREAD_EXTRA_STACKSIZE_PRINTF
- * @ingroup conf
  * @brief Size of the task's printf stack in bytes
  *
  * @note This value must be defined by the CPU specific implementation, please
diff --git a/core/rmutex.c b/core/rmutex.c
index 983ec83434..9438f74f8a 100644
--- a/core/rmutex.c
+++ b/core/rmutex.c
@@ -7,8 +7,7 @@
  */
 
 /**
- * @ingroup     core_sync Synchronization
- * @brief       Recursive Mutex for thread synchronization
+ * @ingroup     core_sync
  * @{
  *
  * @file