diff --git a/t/check-non-portable-shell.pl b/t/check-non-portable-shell.pl
index d5823f71d8..c8f10d40a1 100755
--- a/t/check-non-portable-shell.pl
+++ b/t/check-non-portable-shell.pl
@@ -41,6 +41,7 @@ while (<>) {
 	/^\s*[^#]\s*which\s/ and err 'which is not portable (use type)';
 	/\btest\s+[^=]*==/ and err '"test a == b" is not portable (use =)';
 	/\bwc -l.*"\s*=/ and err '`"$(wc -l)"` is not portable (use test_line_count)';
+	/\bhead\s+-c\b/ and err 'head -c is not portable (use test_copy_bytes BYTES <file >out)';
 	/\bexport\s+[A-Za-z0-9_]*=/ and err '"export FOO=bar" is not portable (use FOO=bar && export FOO)';
 	/^\s*([A-Z0-9_]+=(\w+|(["']).*?\3)\s+)+(\w+)/ and exists($func{$4}) and
 		err '"FOO=bar shell_func" assignment extends beyond "shell_func"';
diff --git a/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh
index 557bd0d0c0..7bff7923f2 100755
--- a/t/t5310-pack-bitmaps.sh
+++ b/t/t5310-pack-bitmaps.sh
@@ -335,7 +335,7 @@ test_expect_success 'truncated bitmap fails gracefully' '
 	git rev-list --use-bitmap-index --count --all >expect &&
 	bitmap=$(ls .git/objects/pack/*.bitmap) &&
 	test_when_finished "rm -f $bitmap" &&
-	head -c 512 <$bitmap >$bitmap.tmp &&
+	test_copy_bytes 512 <$bitmap >$bitmap.tmp &&
 	mv -f $bitmap.tmp $bitmap &&
 	git rev-list --use-bitmap-index --count --all >actual 2>stderr &&
 	test_cmp expect actual &&
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 8bb0f4348e..44288cbb59 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -867,7 +867,7 @@ then
 		# handle only executables, unless they are shell libraries that
 		# need to be in the exec-path.
 		test -x "$1" ||
-		test "# " = "$(head -c 2 <"$1")" ||
+		test "# " = "$(test_copy_bytes 2 <"$1")" ||
 		return;
 
 		base=$(basename "$1")
@@ -882,7 +882,7 @@ then
 		# do not override scripts
 		if test -x "$symlink_target" &&
 		    test ! -d "$symlink_target" &&
-		    test "#!" != "$(head -c 2 < "$symlink_target")"
+		    test "#!" != "$(test_copy_bytes 2 <"$symlink_target")"
 		then
 			symlink_target=../valgrind.sh
 		fi