diff --git a/core/include/thread.h b/core/include/thread.h
index a6108bf862..4f2a1ed3ab 100644
--- a/core/include/thread.h
+++ b/core/include/thread.h
@@ -540,7 +540,7 @@ const char *thread_getname(kernel_pid_t pid);
  *
  * @return          the amount of unused space of the thread's stack
  */
-uintptr_t thread_measure_stack_free(char *stack);
+uintptr_t thread_measure_stack_free(const char *stack);
 #endif /* DEVELHELP */
 
 /**
diff --git a/core/thread.c b/core/thread.c
index 74c2984753..f943a15416 100644
--- a/core/thread.c
+++ b/core/thread.c
@@ -169,7 +169,7 @@ void thread_add_to_list(list_node_t *list, thread_t *thread)
 }
 
 #ifdef DEVELHELP
-uintptr_t thread_measure_stack_free(char *stack)
+uintptr_t thread_measure_stack_free(const char *stack)
 {
     /* Alignment of stack has been fixed (if needed) by thread_create(), so
      * we can silence -Wcast-align here */