diff --git a/psalm-baseline.xml b/psalm-baseline.xml
index d29adab..81b512e 100644
--- a/psalm-baseline.xml
+++ b/psalm-baseline.xml
@@ -3,11 +3,9 @@
   <file src="src/Util/EncodeUtil.php">
     <LessSpecificReturnStatement>
       <code><![CDATA[array_map(hexdec(...), str_split(bin2hex($text), 2))]]></code>
-      <code><![CDATA[pack('C*', ...$bytes)]]></code>
     </LessSpecificReturnStatement>
     <MoreSpecificReturnType>
       <code><![CDATA[NonEmptyByteVector]]></code>
-      <code><![CDATA[non-empty-string]]></code>
     </MoreSpecificReturnType>
   </file>
   <file src="tests/Benchmark/EncoderBench.php">
diff --git a/src/Encoder.php b/src/Encoder.php
index 839bfae..a7d119a 100644
--- a/src/Encoder.php
+++ b/src/Encoder.php
@@ -11,15 +11,14 @@
 
 use function array_map;
 use function array_merge;
-use function array_slice;
 use function array_values;
-use function assert;
 use function count;
 use function implode;
 use function preg_last_error_msg;
 use function preg_match_all;
-use function range;
 use function sprintf;
+use function strlen;
+use function substr;
 
 use const PHP_INT_MAX;
 
@@ -57,8 +56,7 @@ public function encode(string $text): array
                 continue;
             }
 
-            $piece = EncodeUtil::toBytes($match);
-            $rank = $this->vocab->tryGetRank($piece);
+            $rank = $this->vocab->tryGetRank($match);
 
             if ($rank !== null) {
                 $tokens[] = $rank;
@@ -66,7 +64,7 @@ public function encode(string $text): array
                 continue;
             }
 
-            foreach ($this->mergeBytePairs($piece) as $rank) {
+            foreach ($this->mergeBytePairs($match) as $rank) {
                 $tokens[] = $rank;
             }
         }
@@ -101,15 +99,15 @@ public function encodeInChunks(string $text, int $maxTokensPerChunk): array
                 continue;
             }
 
-            $tokenBytes = EncodeUtil::toBytes($match);
-            $mergedBytePairs = $this->mergeBytePairs($tokenBytes);
+            $rank = $this->vocab->tryGetRank($match);
+            $tokens = $rank !== null ? [$rank] : $this->mergeBytePairs($match);
 
-            if (count($tokensInCurrentChunk) + count($mergedBytePairs) > $maxTokensPerChunk) {
+            if (count($tokensInCurrentChunk) + count($tokens) > $maxTokensPerChunk) {
                 $chunks[] = $tokensInCurrentChunk;
                 $tokensInCurrentChunk = [];
             }
 
-            $tokensInCurrentChunk = array_merge($tokensInCurrentChunk, $mergedBytePairs);
+            $tokensInCurrentChunk = array_merge($tokensInCurrentChunk, $tokens);
         }
 
         if (count($tokensInCurrentChunk) > 0) {
@@ -130,38 +128,33 @@ public function decode(array $tokens): string
     }
 
     /**
-     * @psalm-param NonEmptyByteVector $bytes
+     * @param non-empty-string $piece
      *
      * @return list<int>
      */
-    private function mergeBytePairs(array $bytes): array
+    private function mergeBytePairs(string $piece): array
     {
-        /** @var list<array{int, int}> $parts */
-        $parts = array_map(
-            function (int $i) use ($bytes): array {
-                if ($i + 1 < count($bytes)) {
-                    $piece = array_slice($bytes, $i, 2);
-                    assert(count($piece) === 2);
-
-                    return [$i, $this->vocab->tryGetRank($piece) ?? PHP_INT_MAX];
-                }
+        $parts = [];
+
+        for ($i = 0; $i <= strlen($piece); $i++) {
+            $parts[] = [$i, PHP_INT_MAX];
+        }
 
-                return [$i, PHP_INT_MAX];
-            },
-            range(0, count($bytes)),
-        );
-        $getRank = function (array $parts, int $startIndex) use ($bytes): int {
-            if ($startIndex + 2 >= count($parts)) {
+        $getRank = function (array $parts, int $startIndex, int $skip = 0) use (&$piece): int {
+            if (($startIndex + $skip + 2) >= count($parts)) {
                 return PHP_INT_MAX;
             }
 
             $offset = $parts[$startIndex][0];
-            $piece  = array_slice($bytes, $offset, $parts[$startIndex + 2][0] - $offset);
-            assert(count($piece) > 0);
+            $length = $parts[$startIndex + $skip + 2][0] - $offset;
 
-            return $this->vocab->tryGetRank($piece) ?? PHP_INT_MAX;
+            return $this->vocab->tryGetRank(substr($piece, $offset, $length)) ?? PHP_INT_MAX;
         };
 
+        for ($i = 0; $i < count($parts) - 2; $i++) {
+            $parts[$i][1] = $getRank($parts, $i);
+        }
+
         while (count($parts) > 1) {
             $minRank = PHP_INT_MAX;
             $partIndex = 0;
@@ -196,10 +189,10 @@ function (int $i) use ($bytes): array {
         $res = [];
 
         for ($i = 0; $i < $stop; $i++) {
-            $piece = array_slice($bytes, $parts[$i][0], $parts[$i + 1][0] - $parts[$i][0]);
-            assert(count($piece) > 0);
+            $offset = $parts[$i][0];
+            $length = $parts[$i + 1][0] - $offset;
 
-            $res[] = $this->vocab->getRank($piece);
+            $res[] = $this->vocab->getRank(substr($piece, $offset, $length));
         }
 
         return $res;
diff --git a/src/Util/EncodeUtil.php b/src/Util/EncodeUtil.php
index 5c79ebd..94bbc7f 100644
--- a/src/Util/EncodeUtil.php
+++ b/src/Util/EncodeUtil.php
@@ -7,7 +7,6 @@
 use function array_map;
 use function bin2hex;
 use function hexdec;
-use function pack;
 use function str_split;
 
 /** @psalm-type NonEmptyByteVector = non-empty-list<int<0, 255>> */
@@ -22,14 +21,4 @@ public static function toBytes(string $text): array
     {
         return array_map(hexdec(...), str_split(bin2hex($text), 2));
     }
-
-    /**
-     * @psalm-param NonEmptyByteVector $bytes
-     *
-     * @return non-empty-string
-     */
-    public static function fromBytes(array $bytes): string
-    {
-        return pack('C*', ...$bytes);
-    }
 }
diff --git a/src/Vocab/Vocab.php b/src/Vocab/Vocab.php
index fb25f73..9dfb92b 100644
--- a/src/Vocab/Vocab.php
+++ b/src/Vocab/Vocab.php
@@ -104,22 +104,25 @@ public static function fromStream($stream): self
         return new self($map);
     }
 
-    /** @psalm-param NonEmptyByteVector $bytes */
-    public function tryGetRank(array $bytes): int|null
+    public function tryGetRank(string $binary): int|null
     {
-        return $this->tokenToRankMap[EncodeUtil::fromBytes($bytes)] ?? null;
+        if ($binary === '') {
+            throw new InvalidArgumentException('Argument $binary cannot be an empty string');
+        }
+
+        return $this->tokenToRankMap[$binary] ?? null;
     }
 
-    /**
-     * @psalm-param NonEmptyByteVector $bytes
-     *
-     * @throws OutOfBoundsException
-     */
-    public function getRank(array $bytes): int
+    /** @throws OutOfBoundsException */
+    public function getRank(string $binary): int
     {
-        return $this->tokenToRankMap[EncodeUtil::fromBytes($bytes)] ?? throw new OutOfBoundsException(sprintf(
+        if ($binary === '') {
+            throw new InvalidArgumentException('Argument $binary cannot be an empty string');
+        }
+
+        return $this->tokenToRankMap[$binary] ?? throw new OutOfBoundsException(sprintf(
             'No rank for bytes vector: [%s]',
-            implode(', ', $bytes),
+            implode(', ', EncodeUtil::toBytes($binary)),
         ));
     }
 
diff --git a/tests/Vocab/VocabTest.php b/tests/Vocab/VocabTest.php
index 77431c7..8f8d482 100644
--- a/tests/Vocab/VocabTest.php
+++ b/tests/Vocab/VocabTest.php
@@ -5,9 +5,10 @@
 namespace Yethee\Tiktoken\Tests\Vocab;
 
 use PHPUnit\Framework\TestCase;
-use Yethee\Tiktoken\Util\EncodeUtil;
 use Yethee\Tiktoken\Vocab\Vocab;
 
+use function chr;
+
 final class VocabTest extends TestCase
 {
     public function testLoadFromFile(): void
@@ -15,9 +16,9 @@ public function testLoadFromFile(): void
         $vocab = Vocab::fromFile(__DIR__ . '/Fixtures/test.tiktoken');
 
         self::assertCount(47, $vocab);
-        self::assertSame(285, $vocab->getRank(EncodeUtil::toBytes('is')));
+        self::assertSame(285, $vocab->getRank('is'));
         self::assertSame('is', $vocab->getToken(285));
-        self::assertSame(18, $vocab->getRank([51]));
+        self::assertSame(18, $vocab->getRank(chr(51)));
         self::assertSame('3', $vocab->getToken(18));
     }
 }