diff --git a/papers/doc/7-systems/nes.md b/papers/doc/7-systems/nes.md
index 8ce5d808a..45ce95bc3 100644
--- a/papers/doc/7-systems/nes.md
+++ b/papers/doc/7-systems/nes.md
@@ -2,7 +2,7 @@
 
 the console from Nintendo that plays Super Mario Bros. and helped revive the agonizing video game market in the US during mid-80s.
 
-also known as Famicom. It is a five-channel PSG: first two channels play pulse wave with three different duty cycles, third is a fixed-volume triangle channel, fourth is a noise channel (can work in both pseudo-random and periodic modes) and fifth is a (D)PCM sample channel
+also known as Famicom. It is a five-channel PSG: first two channels play pulse wave with three different duty cycles, third is a fixed-volume triangle channel, fourth is a noise channel (can work in both pseudo-random and periodic modes) and fifth is a (D)PCM sample channel.
 
 # effects