diff --git a/config.json b/config.json
index 0cad7cf6..1d0470fa 100644
--- a/config.json
+++ b/config.json
@@ -1236,6 +1236,9 @@
         "prerequisites": [],
         "difficulty": 5
       }
+    ],
+    "foregone": [
+      "parallel-letter-frequency"
     ]
   },
   "concepts": [