diff --git a/mvwrap/mvwrap b/mvwrap/mvwrap
index 963204f..c459276 100755
--- a/mvwrap/mvwrap
+++ b/mvwrap/mvwrap
@@ -170,11 +170,16 @@ sub check_unique (@target_list){
 # Returns an array of unsafe line numbers
 sub check_safety {
 	my ($from, $to) = @_;
-	my ($i, $j, @danger, @unique, %seen);
+	my ($i, $j, @changed, @danger, @unique, %seen);
 	my ($a, $b);
-	for ( $i=0 ; $i < scalar(@$from) ; $i++ ) {
-		for ( $j=0; $j < scalar(@$to); $j++ ) {
-			$a = $from->[$i]; chomp($a);
+	for ($i=0; $i < scalar(@$from); $i++){
+		$a = $from->[$i]; chomp($a);
+		$b = $to->[$i];   chomp($b);
+		push @changed, $i if ($a ne $b);
+	}
+	foreach $i (@changed) {
+		$a = $from->[$i]; chomp($a);
+		for ($j=0; $j < scalar(@$to); $j++){
 			$b = $to->[$j];   chomp($b);
 			if (($a eq $b) && ($i != $j)) {
 				push @danger, $i;
@@ -182,6 +187,7 @@ sub check_safety {
 			}
 		}
 	}
+
 	%seen = ();
 	@unique = grep { ! $seen{$_} ++ } @danger;
 	return @unique;