diff --git a/lib/decoders/fast-png/PNGDecoder.ts b/lib/decoders/fast-png/PNGDecoder.ts
index 4cd0594..eae0df7 100644
--- a/lib/decoders/fast-png/PNGDecoder.ts
+++ b/lib/decoders/fast-png/PNGDecoder.ts
@@ -3,13 +3,14 @@ import { IOBuffer } from './iobuffer/IOBuffer.ts';
 import { Inflate as Inflator } from './pako/index.js';
 
 import { pngSignature, crc } from './common.ts';
-import {
+import type {
   IDecodedPNG,
   DecoderInputType,
   IPNGDecoderOptions,
   PNGDataArray,
   IndexedColors,
   BitDepth,
+  IInflator
 } from './types.ts';
 import {
   ColorType,
@@ -27,7 +28,7 @@ const osIsLittleEndian = uint8[0] === 0xff;
 
 export default class PNGDecoder extends IOBuffer {
   private _checkCrc: boolean;
-  private _inflator: typeof Inflator;
+  private _inflator: IInflator;
   private _png: IDecodedPNG;
   private _end: boolean;
   private _hasPalette: boolean;
@@ -41,7 +42,7 @@ export default class PNGDecoder extends IOBuffer {
     super(data);
     const { checkCrc = false } = options;
     this._checkCrc = checkCrc;
-    this._inflator = new Inflator();
+    this._inflator = <IInflator>new Inflator();
     this._png = {
       width: -1,
       height: -1,
diff --git a/lib/decoders/fast-png/PNGEncoder.ts b/lib/decoders/fast-png/PNGEncoder.ts
index c10f6a0..0ffbb42 100644
--- a/lib/decoders/fast-png/PNGEncoder.ts
+++ b/lib/decoders/fast-png/PNGEncoder.ts
@@ -101,7 +101,7 @@ export default class PNGEncoder extends IOBuffer {
       }
     }
     const buffer = newData.toArray();
-    const compressed = deflate(buffer, this._zlibOptions);
+    const compressed = <Uint8Array>deflate(buffer, this._zlibOptions);
     this.encodeIDAT(compressed);
   }
 
diff --git a/lib/decoders/fast-png/types.ts b/lib/decoders/fast-png/types.ts
index 811e90c..59f6ac3 100644
--- a/lib/decoders/fast-png/types.ts
+++ b/lib/decoders/fast-png/types.ts
@@ -79,3 +79,12 @@ export interface IPNGEncoderOptions {
 }
 
 export type IndexedColors = number[][];
+
+export interface IInflator {
+  result: Uint8Array | Array<any> | string;
+  err: number;
+  msg: string;
+  push: Function;
+  onData: Function;
+  onEnd: Function;
+}