diff --git a/usr.bin/calendar/calendars/calendar.computer b/usr.bin/calendar/calendars/calendar.computer
index 9591f8ca35f5..04f62bb409b6 100644
--- a/usr.bin/calendar/calendars/calendar.computer
+++ b/usr.bin/calendar/calendars/calendar.computer
@@ -51,7 +51,7 @@
 06/23	IBM unbundles software, 1969
 06/23	Turing's Birthday, 1912
 06/30	First advanced degree on computer related topic: to H. Karamanian,
-	Temple Univ., Phila, 1948, for symbolic diffentiation on the ENIAC
+	Temple Univ., Phila, 1948, for symbolic differentiation on the ENIAC
 07/08	Bell Telephone Co. formed (predecessor of AT&T), 1877
 07/08	CDC incorporated, 1957
 08/14	First Unix-based mallet created, 1954