diff --git a/src/index.test.js b/src/index.test.js
index 070d920..47f81c9 100644
--- a/src/index.test.js
+++ b/src/index.test.js
@@ -120,7 +120,7 @@ test('returns false when acTL is not a chunk type', (t) => {
         // Chunk length: 4
         0x00, 0x00, 0x00, 0x04,
         // Chunk type: any
-        0x66, 0x66, 0x66, 0x66,
+        0x00, 0x00, 0x00, 0x01,
         // Chunk data: acTL
         0x61, 0x63, 0x54, 0x4c,
         // Chunk CRC
@@ -151,45 +151,15 @@ test('returns false when next chunk size is too small', (t) => {
         // Chunk length: 4
         0x00, 0x00, 0x00, 0x04,
         // Chunk type: any
-        0x66, 0x66, 0x66, 0x66,
+        0x00, 0x00, 0x00, 0x01,
         // Chunk CRC
         0x00, 0x00, 0x00, 0x00,
         // Chunk length: 4
         0x00, 0x00, 0x00, 0x04,
         // Chunk type: any
-        0x66, 0x66, 0x66, 0x66,
+        0x00, 0x00, 0x00, 0x02,
         // Chunk CRC omitted
       ]),
     ),
   )
 })
-
-test('returns false when chunk type is invalid', (t) => {
-  t.false(
-    isApng(
-      new Uint8Array([
-        // PNG header
-        0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a,
-        // Chunk length: 0
-        0x00, 0x00, 0x00, 0x00,
-        // Chunk type: invalid bytes
-        0x00, 0x00, 0x00, 0x01,
-      ]),
-    ),
-  )
-})
-
-test('returns false when unknown critical chunk type', (t) => {
-  t.false(
-    isApng(
-      new Uint8Array([
-        // PNG header
-        0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a,
-        // Chunk length: 0
-        0x00, 0x00, 0x00, 0x00,
-        // Chunk type: unknown critical
-        0x55, 0x55, 0x55, 0x55,
-      ]),
-    ),
-  )
-})
diff --git a/src/index.ts b/src/index.ts
index d0bf997..bf59464 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,33 +1,11 @@
-function bytesToInt(bytes: Uint8Array): number {
-  return bytes.reduce((value, byte) => (value << 8) + byte, 0)
-}
-
-function chunkTypeToInt(bytes: Uint8Array | number[]): number {
-  if (bytes.length !== headerSizes.TYPE) {
-    throw new Error(`Invalid chunk type size ${bytes.length}`)
-  }
-
-  let value = 0
-  for (let i = 0; i < bytes.length; i++) {
-    const byte = bytes[i]
-
-    if (!(byte >= 0x41 && byte <= 0x5a) && !(byte >= 0x61 && byte <= 0x7a)) {
-      const bytesText = Array.from(bytes)
-        .map((byte) => `0x${byte.toString(16)}`)
-        .join()
-      throw new Error(`Invalid chunk type ${bytesText}`)
-    }
-
-    value = (value << 8) + bytes[i]
-  }
-
-  return value
+function convertToInt(bytes: Uint8Array) {
+  return bytes.reduce((value, byte) => (value << 8) + byte)
 }
 
 function isEqual(
   first: Uint8Array | number[],
   second: Uint8Array | number[],
-  length,
+  length = 4,
 ) {
   while (length > 0) {
     length--
@@ -54,25 +32,10 @@ const headerSizes = {
 
 const chunkTypes = {
   signature: [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a],
-  /** `IHDR` chunk type */
-  imageHeader: chunkTypeToInt([0x49, 0x48, 0x44, 0x52]),
-  /** `PLTE` chunk type */
-  palette: chunkTypeToInt([0x50, 0x4c, 0x54, 0x45]),
-  /** `acTL` chunk type */
-  animationControl: chunkTypeToInt([0x61, 0x63, 0x54, 0x4c]),
-  /** `IDAT` chunk type */
-  imageData: chunkTypeToInt([0x49, 0x44, 0x41, 0x54]),
-  /** `IEND` chunk type */
-  imageEnd: chunkTypeToInt([0x49, 0x45, 0x4e, 0x44]),
+  animationControl: [0x61, 0x63, 0x54, 0x4c], // 'acTL'
+  imageData: [0x49, 0x44, 0x41, 0x54], // 'IDAT'
 }
 
-const knownCriticalChunkTypes = new Set<number>([
-  chunkTypes.imageHeader,
-  chunkTypes.palette,
-  chunkTypes.imageData,
-  chunkTypes.imageEnd,
-])
-
 export default function isApng(buffer: Uint8Array): boolean {
   const minChunkSize = headerSizes.LENGTH + headerSizes.TYPE + headerSizes.CRC
 
@@ -97,29 +60,21 @@ export default function isApng(buffer: Uint8Array): boolean {
    */
 
   while (buffer.length >= minChunkSize) {
-    const chunkType = chunkTypeToInt(
-      buffer.subarray(
-        headerSizes.LENGTH,
-        headerSizes.LENGTH + headerSizes.TYPE,
-      ),
+    const chunkType = buffer.subarray(
+      headerSizes.LENGTH,
+      headerSizes.LENGTH + headerSizes.TYPE,
     )
 
-    // Sixth bit of the first byte of the chunk type is critical property
-    // (0 - critical, 1 - not)
-    const isCriticalChunk = !(chunkType & 0x20000000)
-    if (isCriticalChunk && !knownCriticalChunkTypes.has(chunkType)) {
-      return false
+    if (isEqual(chunkType, chunkTypes.animationControl, headerSizes.TYPE)) {
+      return true
     }
 
-    switch (chunkType) {
-      case chunkTypes.animationControl:
-        return true
-      case chunkTypes.imageData:
-        return false
+    if (isEqual(chunkType, chunkTypes.imageData, headerSizes.TYPE)) {
+      return false
     }
 
     const nextChunkPosition =
-      minChunkSize + bytesToInt(buffer.subarray(0, headerSizes.LENGTH))
+      minChunkSize + convertToInt(buffer.subarray(0, headerSizes.LENGTH))
 
     buffer = buffer.subarray(nextChunkPosition)
   }