diff --git a/src/Utils/Strings.php b/src/Utils/Strings.php
index c25919a79..d66f66f38 100644
--- a/src/Utils/Strings.php
+++ b/src/Utils/Strings.php
@@ -353,51 +353,51 @@ public static function reverse(string $s): string
 
 	/**
 	 * Returns part of $haystack before $nth occurence of $needle (negative value means searching from the end).
-	 * @return string|FALSE  returns FALSE if the needle was not found
+	 * @return string|NULL  returns NULL if the needle was not found
 	 */
 	public static function before(string $haystack, string $needle, int $nth = 1)
 	{
 		$pos = self::pos($haystack, $needle, $nth);
-		return $pos === FALSE
-			? FALSE
+		return $pos === NULL
+			? NULL
 			: substr($haystack, 0, $pos);
 	}
 
 
 	/**
 	 * Returns part of $haystack after $nth occurence of $needle (negative value means searching from the end).
-	 * @return string|FALSE  returns FALSE if the needle was not found
+	 * @return string|NULL  returns NULL if the needle was not found
 	 */
 	public static function after(string $haystack, string $needle, int $nth = 1)
 	{
 		$pos = self::pos($haystack, $needle, $nth);
-		return $pos === FALSE
-			? FALSE
+		return $pos === NULL
+			? NULL
 			: substr($haystack, $pos + strlen($needle));
 	}
 
 
 	/**
 	 * Returns position of $nth occurence of $needle in $haystack (negative value means searching from the end).
-	 * @return int|FALSE  offset in characters or FALSE if the needle was not found
+	 * @return int|NULL  offset in characters or NULL if the needle was not found
 	 */
 	public static function indexOf(string $haystack, string $needle, int $nth = 1)
 	{
 		$pos = self::pos($haystack, $needle, $nth);
-		return $pos === FALSE
-			? FALSE
+		return $pos === NULL
+			? NULL
 			: self::length(substr($haystack, 0, $pos));
 	}
 
 
 	/**
 	 * Returns position of $nth occurence of $needle in $haystack.
-	 * @return int|FALSE  offset in bytes or FALSE if the needle was not found
+	 * @return int|NULL  offset in bytes or NULL if the needle was not found
 	 */
 	private static function pos(string $haystack, string $needle, int $nth = 1)
 	{
 		if (!$nth) {
-			return FALSE;
+			return NULL;
 		} elseif ($nth > 0) {
 			if (strlen($needle) === 0) {
 				return 0;
@@ -416,7 +416,7 @@ private static function pos(string $haystack, string $needle, int $nth = 1)
 				$pos--;
 			}
 		}
-		return $pos;
+		return $pos === FALSE ? NULL : $pos;
 	}
 
 
diff --git a/tests/Utils/Strings.after().phpt b/tests/Utils/Strings.after().phpt
index e333ed5ce..eae7621da 100644
--- a/tests/Utils/Strings.after().phpt
+++ b/tests/Utils/Strings.after().phpt
@@ -27,10 +27,10 @@ test(function () {
 	Assert::same('c', Strings::after($foo, '789', 3));
 	Assert::same('a123456789b123456789c', Strings::after($foo, '9', -3));
 	Assert::same('a123456789b123456789c', Strings::after($foo, '789', -3));
-	Assert::false(Strings::after($foo, '9', 0));
-	Assert::false(Strings::after($foo, 'not-in-string'));
-	Assert::false(Strings::after($foo, 'b', -2));
-	Assert::false(Strings::after($foo, 'b', 2));
+	Assert::null(Strings::after($foo, '9', 0));
+	Assert::null(Strings::after($foo, 'not-in-string'));
+	Assert::null(Strings::after($foo, 'b', -2));
+	Assert::null(Strings::after($foo, 'b', 2));
 });
 
 
diff --git a/tests/Utils/Strings.before().phpt b/tests/Utils/Strings.before().phpt
index 1866dcfa2..68eff6cfc 100644
--- a/tests/Utils/Strings.before().phpt
+++ b/tests/Utils/Strings.before().phpt
@@ -26,10 +26,10 @@ test(function () {
 	Assert::same('0123456789a123456789b123456', Strings::before($foo, '789', 3));
 	Assert::same('012345678', Strings::before($foo, '9', -3));
 	Assert::same('0123456', Strings::before($foo, '789', -3));
-	Assert::false(Strings::before($foo, '9', 0));
-	Assert::false(Strings::before($foo, 'not-in-string'));
-	Assert::false(Strings::before($foo, 'b', -2));
-	Assert::false(Strings::before($foo, 'b', 2));
+	Assert::null(Strings::before($foo, '9', 0));
+	Assert::null(Strings::before($foo, 'not-in-string'));
+	Assert::null(Strings::before($foo, 'b', -2));
+	Assert::null(Strings::before($foo, 'b', 2));
 });
 
 
diff --git a/tests/Utils/Strings.indexOf().phpt b/tests/Utils/Strings.indexOf().phpt
index eceae79d9..8738b0386 100644
--- a/tests/Utils/Strings.indexOf().phpt
+++ b/tests/Utils/Strings.indexOf().phpt
@@ -27,10 +27,10 @@ test(function () {
 	Assert::same(27, Strings::indexOf($foo, '789', 3));
 	Assert::same(9, Strings::indexOf($foo, '9', -3));
 	Assert::same(7, Strings::indexOf($foo, '789', -3));
-	Assert::false(Strings::indexOf($foo, '9', 0));
-	Assert::false(Strings::indexOf($foo, 'not-in-string'));
-	Assert::false(Strings::indexOf($foo, 'b', -2));
-	Assert::false(Strings::indexOf($foo, 'b', 2));
+	Assert::null(Strings::indexOf($foo, '9', 0));
+	Assert::null(Strings::indexOf($foo, 'not-in-string'));
+	Assert::null(Strings::indexOf($foo, 'b', -2));
+	Assert::null(Strings::indexOf($foo, 'b', 2));
 });