diff --git a/packages/transducers/src/iterator.ts b/packages/transducers/src/iterator.ts
index 43f32df6d3..22ddd8c6d6 100644
--- a/packages/transducers/src/iterator.ts
+++ b/packages/transducers/src/iterator.ts
@@ -38,7 +38,7 @@ export function* iterator<A, B>(xform: Transducer<A, B>, xs: Iterable<A>): Itera
  * @param xs
  */
 export function* iterator1<A, B>(xform: Transducer<A, B>, xs: Iterable<A>): IterableIterator<B> {
-    const reduce = (<Reducer<B, A>>xform([null, null, (acc, x) => (acc = x)]))[2];
+    const reduce = (<Reducer<B, A>>xform([null, null, (_, x) => x]))[2];
     for (let x of xs) {
         let y = reduce(<any>SEMAPHORE, x);
         if (isReduced(y)) {
diff --git a/packages/transducers/src/xform/interleave.ts b/packages/transducers/src/xform/interleave.ts
index 526c1d2b18..0d773928fb 100644
--- a/packages/transducers/src/xform/interleave.ts
+++ b/packages/transducers/src/xform/interleave.ts
@@ -5,12 +5,12 @@ import { isReduced } from "../reduced";
 
 export function interleave<A, B>(sep: B | (() => B)): Transducer<A, A | B>;
 export function interleave<A, B>(sep: B | (() => B), src: Iterable<A>): IterableIterator<A | B>;
-export function interleave<A, B>(sep: B | (() => B), src?: Iterable<A>): any {
+export function interleave<A, B>(sep: any, src?: Iterable<A>): any {
     return src ?
         iterator(interleave(sep), src) :
         (rfn: Reducer<any, A | B>) => {
             const r = rfn[2];
-            const _sep = typeof sep === "function" ? sep : () => sep;
+            const _sep: () => B = typeof sep === "function" ? sep : () => sep;
             return compR(rfn,
                 (acc, x: A) => {
                     acc = r(acc, _sep());
diff --git a/packages/transducers/src/xform/interpose.ts b/packages/transducers/src/xform/interpose.ts
index daab88ac73..200fb0ecb9 100644
--- a/packages/transducers/src/xform/interpose.ts
+++ b/packages/transducers/src/xform/interpose.ts
@@ -5,12 +5,12 @@ import { isReduced } from "../reduced";
 
 export function interpose<A, B>(sep: B | (() => B)): Transducer<A, A | B>;
 export function interpose<A, B>(sep: B | (() => B), src: Iterable<A>): IterableIterator<A | B>;
-export function interpose<A, B>(sep: B | (() => B), src?: Iterable<A>): any {
+export function interpose<A, B>(sep: any, src?: Iterable<A>): any {
     return src ?
         iterator(interpose(sep), src) :
         (rfn: Reducer<any, A | B>) => {
             const r = rfn[2];
-            const _sep = typeof sep === "function" ? sep : () => sep;
+            const _sep: () => B = typeof sep === "function" ? sep : () => sep;
             let first = true;
             return compR(rfn,
                 (acc, x: A) => {