diff --git a/t/lib-terminal.sh b/t/lib-terminal.sh
index 9a2dca506a..51845491bb 100644
--- a/t/lib-terminal.sh
+++ b/t/lib-terminal.sh
@@ -1,6 +1,20 @@
 # Helpers for terminal output tests.
 
-test_expect_success PERL 'set up terminal for tests' '
+# Catch tests which should depend on TTY but forgot to. There's no need
+# to aditionally check that the TTY prereq is set here.  If the test declared
+# it and we are running the test, then it must have been set.
+test_terminal () {
+	if ! test_declared_prereq TTY
+	then
+		echo >&4 "test_terminal: need to declare TTY prerequisite"
+		return 127
+	fi
+	perl "$TEST_DIRECTORY"/test-terminal.perl "$@"
+}
+
+test_lazy_prereq TTY '
+	test_have_prereq PERL &&
+
 	# Reading from the pty master seems to get stuck _sometimes_
 	# on Mac OS X 10.5.0, using Perl 5.10.0 or 5.8.9.
 	#
@@ -15,21 +29,8 @@ test_expect_success PERL 'set up terminal for tests' '
 	# After 2000 iterations or so it hangs.
 	# https://rt.cpan.org/Ticket/Display.html?id=65692
 	#
-	if test "$(uname -s)" = Darwin
-	then
-		:
-	elif
-		perl "$TEST_DIRECTORY"/test-terminal.perl \
-			sh -c "test -t 1 && test -t 2"
-	then
-		test_set_prereq TTY &&
-		test_terminal () {
-			if ! test_declared_prereq TTY
-			then
-				echo >&4 "test_terminal: need to declare TTY prerequisite"
-				return 127
-			fi
-			perl "$TEST_DIRECTORY"/test-terminal.perl "$@"
-		}
-	fi
+	test "$(uname -s)" != Darwin &&
+
+	perl "$TEST_DIRECTORY"/test-terminal.perl \
+		sh -c "test -t 1 && test -t 2"
 '