diff --git a/src/Enum/KeyType.php b/src/Enum/KeyType.php
index efd042a..235771f 100644
--- a/src/Enum/KeyType.php
+++ b/src/Enum/KeyType.php
@@ -38,7 +38,8 @@ class KeyType {
 
 		// a = 0x61
 		// z = 0x7a
-		if ($ord >= 0x61 && $ord <= 0x7a)
+		// So, 0x60 < $ord < 0x7b
+		if ($ord > 0x60 && $ord < 0x7b)
 		{
 			return chr(ctrl_key($char));
 		}
diff --git a/tests/Enum/KeyTypeTest.php b/tests/Enum/KeyTypeTest.php
new file mode 100644
index 0000000..c787548
--- /dev/null
+++ b/tests/Enum/KeyTypeTest.php
@@ -0,0 +1,35 @@
+<?php declare(strict_types=1);
+
+namespace Aviat\Kilo\Tests\Enum;
+
+use Aviat\Kilo\Enum\KeyType;
+use PHPUnit\Framework\TestCase;
+
+class KeyTypeTest extends TestCase {
+	public function testSanityCheck(): void
+	{
+		for ($i = 1; $i < 27; $i++)
+		{
+			$char = chr(0x60 + $i);
+			$ord = $i;
+			$expected = chr($ord);
+
+			$actual = KeyType::CTRL($char);
+
+			$this->assertEquals($expected, $actual, "CTRL + '{$char}' should return chr($ord)");
+		}
+	}
+
+	public function testNullOnInvalidChar(): void
+	{
+		$this->assertNull(KeyType::CTRL("\t"));
+	}
+
+	public function testSameOutputOnUpperOrLower(): void
+	{
+		$lower = KeyType::CTRL('v');
+		$upper = KeyType::CTRL('V');
+
+		$this->assertEquals($lower, $upper);
+	}
+}