diff --git a/lttb-impl-notes.md b/lttb-impl-notes.md
index b439f72..603d1f3 100644
--- a/lttb-impl-notes.md
+++ b/lttb-impl-notes.md
@@ -109,7 +109,7 @@ Mathematical expression and intrinsic function application engine. Accepts a sin
     - Push `NORM(VARS[C])` to `VALSTACK`.
     - Set `PREVC = C`, increment `I`, go to step 6.
 12. If `C` is `(`:
-    - Push `(` to OPSTACK.
+    - Push `(` to `OPSTACK`.
     - Set `PREVC = C`, increment `I`, go to step 6.
 13. If `C` is `)`:
     - While `OPSTACK` top is not `(`: Execute `EVALHELPER(VALSTACK, OPSTACK)`.