diff --git a/doc/lettable-operators.md b/doc/lettable-operators.md
index eb2c84bcb6..d2b8f56d71 100644
--- a/doc/lettable-operators.md
+++ b/doc/lettable-operators.md
@@ -81,3 +81,25 @@ interval(1000).pipe(
 .subscribe(x => console.log(x));
 // [0, 12, 24]
 ```
+
+## Known Issues
+
+In TypeScript 2.3 and lower, typings will need to be added to functions passed to operators, as types cannot be inferred prior to TypeScript 2.4. In TypeScript 2.4, types will infer via composition properly.
+
+**TS 2.3 and under**
+
+```ts
+range(0, 10).pipe(
+  map((n: number) => n + '!'),
+  map((s: string) => 'Hello, ' + s),
+).subscribe(x => console.log(x))
+```
+
+**TS 2.4 and up**
+
+```ts
+range(0, 10).pipe(
+  map(n => n + '!'),
+  map(s => 'Hello, ' + s),
+).subscribe(x => console.log(x))
+```