diff --git a/src/Tokenizers/PHP.php b/src/Tokenizers/PHP.php
index 6e3ebdb6ae..dded2a5c17 100644
--- a/src/Tokenizers/PHP.php
+++ b/src/Tokenizers/PHP.php
@@ -2718,6 +2718,8 @@ protected function processAdditional()
                         T_NAMESPACE         => T_NAMESPACE,
                         T_NS_SEPARATOR      => T_NS_SEPARATOR,
                         T_NULL              => T_NULL,
+                        T_TRUE              => T_TRUE,
+                        T_FALSE             => T_FALSE,
                         T_NULLABLE          => T_NULLABLE,
                         T_PARENT            => T_PARENT,
                         T_SELF              => T_SELF,
diff --git a/tests/Core/Tokenizer/BackfillFnTokenTest.inc b/tests/Core/Tokenizer/BackfillFnTokenTest.inc
index 13f165b77f..6cf44229cc 100644
--- a/tests/Core/Tokenizer/BackfillFnTokenTest.inc
+++ b/tests/Core/Tokenizer/BackfillFnTokenTest.inc
@@ -92,12 +92,27 @@ fn(array $a) : array => $a;
 /* testStaticReturnType */
 fn(array $a) : static => $a;
 
+/* testFalseReturnType */
+fn(array $a) : false => $a;
+
+/* testTrueReturnType */
+fn(array $a) : True => $a;
+
+/* testNullReturnType */
+fn(array $a) : null => $a;
+
 /* testUnionParamType */
 $arrowWithUnionParam = fn(int|float $param) : SomeClass => new SomeClass($param);
 
 /* testUnionReturnType */
 $arrowWithUnionReturn = fn($param) : int|float => $param | 10;
 
+/* testUnionReturnTypeWithTrue */
+$arrowWithUnionReturn = fn($param) : int|true => $param | 10;
+
+/* testUnionReturnTypeWithFalse */
+$arrowWithUnionReturn = fn($param) : string|FALSE => $param | 10;
+
 /* testTernary */
 $fn = fn($a) => $a ? /* testTernaryThen */ fn() : string => 'a' : /* testTernaryElse */ fn() : string => 'b';
 
diff --git a/tests/Core/Tokenizer/BackfillFnTokenTest.php b/tests/Core/Tokenizer/BackfillFnTokenTest.php
index d6d77c7681..5ad4e1b95a 100644
--- a/tests/Core/Tokenizer/BackfillFnTokenTest.php
+++ b/tests/Core/Tokenizer/BackfillFnTokenTest.php
@@ -437,6 +437,15 @@ public static function dataKeywordReturnTypes()
             'static'   => [
                 'testMarker'  => '/* testStaticReturnType */',
             ],
+            'false'    => [
+                'testMarker'  => '/* testFalseReturnType */',
+            ],
+            'true'     => [
+                'testMarker'  => '/* testTrueReturnType */',
+            ],
+            'null'     => [
+                'testMarker'  => '/* testNullReturnType */',
+            ],
         ];
 
     }//end dataKeywordReturnTypes()
@@ -474,6 +483,38 @@ public function testUnionReturnType()
     }//end testUnionReturnType()
 
 
+    /**
+     * Test arrow function with a union return type.
+     *
+     * @covers PHP_CodeSniffer\Tokenizers\PHP::processAdditional
+     *
+     * @return void
+     */
+    public function testUnionReturnTypeWithTrue()
+    {
+        $token = $this->getTargetToken('/* testUnionReturnTypeWithTrue */', T_FN);
+        $this->backfillHelper($token);
+        $this->scopePositionTestHelper($token, 11, 18);
+
+    }//end testUnionReturnTypeWithTrue()
+
+
+    /**
+     * Test arrow function with a union return type.
+     *
+     * @covers PHP_CodeSniffer\Tokenizers\PHP::processAdditional
+     *
+     * @return void
+     */
+    public function testUnionReturnTypeWithFalse()
+    {
+        $token = $this->getTargetToken('/* testUnionReturnTypeWithFalse */', T_FN);
+        $this->backfillHelper($token);
+        $this->scopePositionTestHelper($token, 11, 18);
+
+    }//end testUnionReturnTypeWithFalse()
+
+
     /**
      * Test arrow functions used in ternary operators.
      *