diff --git a/src/tetras-back b/src/tetras-back
index 81d8be723d4acfe567634f64b011f3700340d6ad..39c3a7defd57e41e5b1cc3fea28405a5bd02f24e 100755
--- a/src/tetras-back
+++ b/src/tetras-back
@@ -244,7 +244,7 @@ sub format_log{
     my %args = @_;
     my $date = strftime("%F %X", localtime());
     my $string = "$date\t$args{level}\t$args{message}\n";
-    if( not utf8::is_unicode($string)){
+    if( not utf8::is_utf8($string)){
         utf8::encode($string);
     }
     return $string;