diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 377f08a142..c4b4d3a4c7 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -1640,17 +1640,7 @@ test_match_signal () {
 
 # Read up to "$1" bytes (or to EOF) from stdin and write them to stdout.
 test_copy_bytes () {
-	perl -e '
-		my $len = $ARGV[1];
-		while ($len > 0) {
-			my $s;
-			my $nread = sysread(STDIN, $s, $len);
-			die "cannot read: $!" unless defined($nread);
-			last unless $nread;
-			print $s;
-			$len -= $nread;
-		}
-	' - "$1"
+	dd ibs=1 count="$1" 2>/dev/null
 }
 
 # run "$@" inside a non-git directory