diff --git a/mod.ts b/mod.ts
index 18faa9f..c2c0eb8 100644
--- a/mod.ts
+++ b/mod.ts
@@ -341,17 +341,16 @@ export function ifilter<T>(
 /**
  * Apply map, and filter invalid results in the same pass.
  */
-export function imapfilter<T1, T2, E>(
+export function imapfilter<T1, T2>(
   iterable: Iterable<T1>,
-  mapfunc: (_: T1) => Exclude<T2, E> | typeof exclusion,
-  exclusion: E = null as unknown as E,
-): Iterable<T2> {
+  mapfunc: (_: T1) => T2 | null,
+): Iterable<Exclude<T2, null>> {
   return {
     [Symbol.iterator]: function* () {
       for (let value of iterable) {
         const mapped = mapfunc(value);
-        if (mapped !== exclusion) {
-          yield mapped as T2;
+        if (mapped !== null) {
+          yield mapped as Exclude<T2, null>;
         }
       }
     },