diff --git a/composer.json b/composer.json
index 3ea181d..602a473 100644
--- a/composer.json
+++ b/composer.json
@@ -13,7 +13,7 @@
     "require": {
         "php": "^7.4 || ^8.0",
         "php-stubs/wordpress-stubs": "^6.6.2",
-        "phpstan/phpstan": "^2.0"
+        "phpstan/phpstan": "^2.1.18"
     },
     "require-dev": {
         "composer/composer": "^2.1.14",
diff --git a/extension.neon b/extension.neon
index 00a8965..79ec298 100644
--- a/extension.neon
+++ b/extension.neon
@@ -21,6 +21,10 @@ services:
         class: SzepeViktor\PHPStan\WordPress\StripslashesFromStringsOnlyDynamicFunctionReturnTypeExtension
         tags:
             - phpstan.broker.dynamicFunctionReturnTypeExtension
+    -
+        class: SzepeViktor\PHPStan\WordPress\SlashitFunctionsDynamicFunctionReturnTypeExtension
+        tags:
+            - phpstan.broker.dynamicFunctionReturnTypeExtension
     -
         class: SzepeViktor\PHPStan\WordPress\WpParseUrlFunctionDynamicReturnTypeExtension
         tags:
diff --git a/phpcs.xml.dist b/phpcs.xml.dist
index c71d768..f4d17ce 100644
--- a/phpcs.xml.dist
+++ b/phpcs.xml.dist
@@ -25,6 +25,7 @@
 
     <!-- TypeTraverser uses callable $traverse -->
     <rule ref="NeutronStandard.Functions.VariableFunctions.VariableFunction">
+        <exclude-pattern>src/SlashitFunctionsDynamicFunctionReturnTypeExtension.php</exclude-pattern>
         <exclude-pattern>src/StripslashesFromStringsOnlyDynamicFunctionReturnTypeExtension.php</exclude-pattern>
         <exclude-pattern>src/WpSlashDynamicFunctionReturnTypeExtension.php</exclude-pattern>
     </rule>
diff --git a/src/SlashitFunctionsDynamicFunctionReturnTypeExtension.php b/src/SlashitFunctionsDynamicFunctionReturnTypeExtension.php
new file mode 100644
index 0000000..3c51687
--- /dev/null
+++ b/src/SlashitFunctionsDynamicFunctionReturnTypeExtension.php
@@ -0,0 +1,97 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SzepeViktor\PHPStan\WordPress;
+
+use PhpParser\Node\Arg;
+use PhpParser\Node\Expr\BinaryOp\Concat;
+use PhpParser\Node\Expr\FuncCall;
+use PhpParser\Node\Name\FullyQualified;
+use PhpParser\Node\Scalar\String_;
+use PHPStan\Analyser\Scope;
+use PHPStan\Node\Expr\TypeExpr;
+use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Type\Accessory\AccessoryNonFalsyStringType;
+use PHPStan\Type\Constant\ConstantStringType;
+use PHPStan\Type\GeneralizePrecision;
+use PHPStan\Type\IntersectionType;
+use PHPStan\Type\Type;
+use PHPStan\Type\TypeTraverser;
+use PHPStan\Type\UnionType;
+
+final class SlashitFunctionsDynamicFunctionReturnTypeExtension implements \PHPStan\Type\DynamicFunctionReturnTypeExtension
+{
+    use NormalizedArguments;
+
+    public function isFunctionSupported(FunctionReflection $functionReflection): bool
+    {
+        return in_array(
+            $functionReflection->getName(),
+            [
+                'backslashit',
+                'trailingslashit',
+                'untrailingslashit',
+            ],
+            true
+        );
+    }
+
+    /**
+     * @see https://developer.wordpress.org/reference/functions/backslashit/
+     * @see https://developer.wordpress.org/reference/functions/trailingslashit/
+     * @see https://developer.wordpress.org/reference/functions/untrailingslashit/
+     */
+    public function getTypeFromFunctionCall(FunctionReflection $functionReflection, FuncCall $functionCall, Scope $scope): ?Type
+    {
+        if (count($functionCall->getArgs()) === 0) {
+            return null;
+        }
+
+        $argType = $scope->isDeclareStrictTypes()
+            ? $scope->getType($functionCall->getArgs()[0]->value)
+            : $scope->getType($functionCall->getArgs()[0]->value)->toString();
+
+        if (! $argType->isString()->yes()) {
+            return null;
+        }
+
+        $functionName = $functionReflection->getName();
+
+        if (strpos($functionName, 'trailingslashit') !== false) {
+            $type = $scope->getType(new FuncCall(new FullyQualified('rtrim'), [$functionCall->getArgs()[0], new Arg(new String_('/\\'))]));
+
+            if ($functionName === 'untrailingslashit') {
+                return $type;
+            }
+
+            return $scope->getType(new Concat(new TypeExpr($type), new String_('/')));
+        }
+
+        if (! ($functionName === 'backslashit')) {
+            return null;
+        }
+
+        return TypeTraverser::map(
+            $argType,
+            static function (Type $type, callable $traverse): Type {
+                if ($type instanceof UnionType || $type instanceof IntersectionType) {
+                    return $traverse($type);
+                }
+
+                if ($type instanceof ConstantStringType) {
+                    if ($type->getValue() === '') {
+                        return $type;
+                    }
+                    return $traverse($type->generalize(GeneralizePrecision::moreSpecific()));
+                }
+
+                if ($type->isNumericString()->or($type->isNonEmptyString())->yes()) {
+                    return new AccessoryNonFalsyStringType();
+                }
+
+                return $type;
+            }
+        );
+    }
+}
diff --git a/src/StripslashesFromStringsOnlyDynamicFunctionReturnTypeExtension.php b/src/StripslashesFromStringsOnlyDynamicFunctionReturnTypeExtension.php
index c556a15..8be0360 100644
--- a/src/StripslashesFromStringsOnlyDynamicFunctionReturnTypeExtension.php
+++ b/src/StripslashesFromStringsOnlyDynamicFunctionReturnTypeExtension.php
@@ -4,8 +4,11 @@
 
 namespace SzepeViktor\PHPStan\WordPress;
 
+use PhpParser\Node\Arg;
 use PhpParser\Node\Expr\FuncCall;
+use PhpParser\Node\Name\FullyQualified;
 use PHPStan\Analyser\Scope;
+use PHPStan\Node\Expr\TypeExpr;
 use PHPStan\Reflection\FunctionReflection;
 use PHPStan\Type\Constant\ConstantStringType;
 use PHPStan\Type\Type;
@@ -32,16 +35,25 @@ public function getTypeFromFunctionCall(FunctionReflection $functionReflection,
 
         return TypeTraverser::map(
             $argType,
-            static function (Type $type, callable $traverse): Type {
+            static function (Type $type, callable $traverse) use ($scope): Type {
                 if ($type instanceof UnionType) {
                     return $traverse($type);
                 }
 
+                if (! $type->isString()->yes()) {
+                    return $type;
+                }
+
                 if ($type instanceof ConstantStringType) {
                     return new ConstantStringType(stripslashes($type->getValue()));
                 }
 
-                return $type;
+                return $scope->getType(
+                    new FuncCall(
+                        new FullyQualified('stripslashes'),
+                        [new Arg(new TypeExpr($type))]
+                    )
+                );
             }
         );
     }
diff --git a/tests/DynamicReturnTypeExtensionTest.php b/tests/DynamicReturnTypeExtensionTest.php
index 2b09ef1..4f3df6c 100644
--- a/tests/DynamicReturnTypeExtensionTest.php
+++ b/tests/DynamicReturnTypeExtensionTest.php
@@ -12,13 +12,14 @@ class DynamicReturnTypeExtensionTest extends \PHPStan\Testing\TypeInferenceTestC
     public function dataFileAsserts(): iterable
     {
         // Path to a file with actual asserts of expected types:
-        yield from self::gatherAssertTypes(__DIR__ . '/data/apply_filters.php');
+        yield from self::gatherAssertTypes(__DIR__ . '/data/apply-filters.php');
         yield from self::gatherAssertTypes(__DIR__ . '/data/ApplyFiltersTestClass.php');
-        yield from self::gatherAssertTypes(__DIR__ . '/data/esc_sql.php');
+        yield from self::gatherAssertTypes(__DIR__ . '/data/esc-sql.php');
         yield from self::gatherAssertTypes(__DIR__ . '/data/normalize-whitespace.php');
-        yield from self::gatherAssertTypes(__DIR__ . '/data/shortcode_atts.php');
+        yield from self::gatherAssertTypes(__DIR__ . '/data/shortcode-atts.php');
+        yield from self::gatherAssertTypes(__DIR__ . '/data/slashit-functions.php');
         yield from self::gatherAssertTypes(__DIR__ . '/data/stripslashes-from-strings-only.php');
-        yield from self::gatherAssertTypes(__DIR__ . '/data/wp_parse_url.php');
+        yield from self::gatherAssertTypes(__DIR__ . '/data/wp-parse-url.php');
         yield from self::gatherAssertTypes(__DIR__ . '/data/wp-slash.php');
     }
 
diff --git a/tests/data/apply_filters.php b/tests/data/apply-filters.php
similarity index 100%
rename from tests/data/apply_filters.php
rename to tests/data/apply-filters.php
diff --git a/tests/data/esc_sql.php b/tests/data/esc-sql.php
similarity index 100%
rename from tests/data/esc_sql.php
rename to tests/data/esc-sql.php
diff --git a/tests/data/shortcode_atts.php b/tests/data/shortcode-atts.php
similarity index 100%
rename from tests/data/shortcode_atts.php
rename to tests/data/shortcode-atts.php
diff --git a/tests/data/slashit-functions.php b/tests/data/slashit-functions.php
new file mode 100644
index 0000000..aeefc1b
--- /dev/null
+++ b/tests/data/slashit-functions.php
@@ -0,0 +1,73 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SzepeViktor\PHPStan\WordPress\Tests;
+
+use function backslashit;
+use function trailingslashit;
+use function untrailingslashit;
+use function PHPStan\Testing\assertType;
+
+/*
+ * trailingslashit()
+ */
+
+assertType("'/'", trailingslashit(''));
+assertType("'0/'", trailingslashit('0'));
+assertType("'foo/'", trailingslashit('foo'));
+assertType("'foo/'", trailingslashit('foo/'));
+assertType("'foo/'", trailingslashit('foo//'));
+assertType("'foo/'", trailingslashit('foo\\'));
+
+/** @var non-empty-string $nonEmptyString */
+assertType('non-falsy-string', trailingslashit($nonEmptyString));
+
+/** @var non-falsy-string $nonFalsyString */
+assertType('non-falsy-string', trailingslashit($nonFalsyString));
+
+/** @var lowercase-string&non-empty-string $lowercaseNonEmptyString */
+assertType('lowercase-string&non-falsy-string', trailingslashit($lowercaseNonEmptyString));
+
+/*
+ * untrailingslashit()
+ */
+
+assertType("''", untrailingslashit(''));
+assertType("'0'", untrailingslashit('0'));
+assertType("'foo'", untrailingslashit('foo'));
+assertType("'foo'", untrailingslashit('foo/'));
+assertType("'foo'", untrailingslashit('foo//'));
+assertType("'foo'", untrailingslashit('foo\\'));
+
+/** @var non-empty-string $nonEmptyString */
+assertType('string', untrailingslashit($nonEmptyString));
+
+/** @var non-falsy-string $nonFalsyString */
+assertType('string', untrailingslashit($nonFalsyString));
+
+/** @var lowercase-string&non-empty-string $lowercaseNonEmptyString */
+assertType('lowercase-string', untrailingslashit($lowercaseNonEmptyString));
+
+/*
+ * backslashit()
+ */
+
+assertType("''", backslashit(''));
+assertType('literal-string&lowercase-string&non-falsy-string&uppercase-string', backslashit('0'));
+assertType('literal-string&lowercase-string&non-falsy-string', backslashit('foo'));
+
+/** @var non-empty-string $nonEmptyString */
+assertType('non-falsy-string', backslashit($nonEmptyString));
+
+/** @var non-falsy-string $nonFalsyString */
+assertType('non-falsy-string', backslashit($nonFalsyString));
+
+/** @var lowercase-string&non-empty-string $lowercaseNonEmptyString */
+assertType('lowercase-string&non-falsy-string', backslashit($lowercaseNonEmptyString));
+
+/** @var numeric-string $numericString */
+assertType('non-falsy-string', backslashit($numericString));
+
+/** @var string $aString */
+assertType('string', backslashit($aString));
diff --git a/tests/data/stripslashes-from-strings-only.php b/tests/data/stripslashes-from-strings-only.php
index e6ea1ad..25daeac 100644
--- a/tests/data/stripslashes-from-strings-only.php
+++ b/tests/data/stripslashes-from-strings-only.php
@@ -10,8 +10,12 @@
 assertType("''", stripslashes_from_strings_only(''));
 assertType("'foo'", stripslashes_from_strings_only('foo'));
 assertType("'foo\'s bar'", stripslashes_from_strings_only('foo\'s bar'));
+/** @var non-empty-string $value */
+assertType('string', stripslashes_from_strings_only($value));
+/** @var non-falsy-string $value */
+assertType('string', stripslashes_from_strings_only($value));
 /** @var lowercase-string $value */
-assertType('lowercase-string', stripslashes_from_strings_only($value));
+assertType('string', stripslashes_from_strings_only($value));
 
 assertType('array{}', stripslashes_from_strings_only([]));
 assertType("array{'foo'}", stripslashes_from_strings_only(['foo']));
diff --git a/tests/data/wp_parse_url.php b/tests/data/wp-parse-url.php
similarity index 100%
rename from tests/data/wp_parse_url.php
rename to tests/data/wp-parse-url.php