1 files changed, 13 insertions, 9 deletions
diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 8a3e3f3e22..7ab07fe6a2 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -17421,20 +17421,24 @@ static void f_writefile(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 
   bool binary = false;
   bool append = false;
-  bool do_fsync = true;
+  bool do_fsync = !!p_fs;
   if (argvars[2].v_type != VAR_UNKNOWN) {
     const char *const flags = tv_get_string_chk(&argvars[2]);
     if (flags == NULL) {
       return;
     }
-    if (strchr(flags, 'b')) {
-      binary = true;
-    }
-    if (strchr(flags, 'a')) {
-      append = true;
-    }
-    if (strchr(flags, 'S')) {
-      do_fsync = false;
+    for (const char *p = flags; *p; p++) {
+      switch (*p) {
+        case 'b': { binary = true; break; }
+        case 'a': { append = true; break; }
+        case 's': { do_fsync = true; break; }
+        case 'S': { do_fsync = false; break; }
+        default: {
+          // Using %s, p and not %c, *p to preserve multibyte characters
+          emsgf(_("E5060: Unknown flag: %s"), p);
+          return;
+        }
+      }
     }
   }