diff --git a/RichString.c b/RichString.c
index 248b3ae04..390beb073 100644
--- a/RichString.c
+++ b/RichString.c
@@ -64,7 +64,7 @@ void RichString_rewind(RichString* this, int count) {
 
 #ifdef HAVE_LIBNCURSESW
 
-static size_t mbstowcs_nonfatal(wchar_t* dest, const char* src, size_t n) {
+static size_t mbstowcs_nonfatal(wchar_t* restrict dest, const char* restrict src, size_t n) {
    size_t written = 0;
    mbstate_t ps = { 0 };
    bool broken = false;