diff --git a/src/Fixer/PhpUnit/PhpUnitDedicateAssertFixer.php b/src/Fixer/PhpUnit/PhpUnitDedicateAssertFixer.php
index 4d999f9f5ba..024f0a49d73 100644
--- a/src/Fixer/PhpUnit/PhpUnitDedicateAssertFixer.php
+++ b/src/Fixer/PhpUnit/PhpUnitDedicateAssertFixer.php
@@ -24,6 +24,7 @@
 use PhpCsFixer\FixerDefinition\FixerDefinitionInterface;
 use PhpCsFixer\Tokenizer\Analyzer\ArgumentsAnalyzer;
 use PhpCsFixer\Tokenizer\Analyzer\FunctionsAnalyzer;
+use PhpCsFixer\Tokenizer\CT;
 use PhpCsFixer\Tokenizer\Token;
 use PhpCsFixer\Tokenizer\Tokens;
 
@@ -286,6 +287,10 @@ private function fixAssertTrueFalse(Tokens $tokens, ArgumentsAnalyzer $arguments
         $testIndex = $tokens->getNextMeaningfulToken($assertCall['openBraceIndex']);
 
         if (!$tokens[$testIndex]->isGivenKind([T_EMPTY, T_STRING])) {
+            if ($this->fixAssertTrueFalseInstanceof($tokens, $assertCall, $testIndex)) {
+                return;
+            }
+
             if (!$tokens[$testIndex]->isGivenKind(T_NS_SEPARATOR)) {
                 return;
             }
@@ -370,6 +375,66 @@ private function fixAssertTrueFalse(Tokens $tokens, ArgumentsAnalyzer $arguments
         }
     }
 
+    private function fixAssertTrueFalseInstanceof(Tokens $tokens, array $assertCall, int $testIndex): bool
+    {
+        if ($tokens[$testIndex]->equals('!')) {
+            $variableIndex = $tokens->getNextMeaningfulToken($testIndex);
+            $positive = false;
+        } else {
+            $variableIndex = $testIndex;
+            $positive = true;
+        }
+
+        if (!$tokens[$variableIndex]->isGivenKind(T_VARIABLE)) {
+            return false;
+        }
+
+        $instanceOfIndex = $tokens->getNextMeaningfulToken($variableIndex);
+
+        if (!$tokens[$instanceOfIndex]->isGivenKind(T_INSTANCEOF)) {
+            return false;
+        }
+
+        $classEndIndex = $instanceOfIndex;
+        $classPartTokens = [];
+
+        do {
+            $classEndIndex = $tokens->getNextMeaningfulToken($classEndIndex);
+            $classPartTokens[] = $tokens[$classEndIndex];
+        } while ($tokens[$classEndIndex]->isGivenKind([T_STRING, T_NS_SEPARATOR, T_VARIABLE]));
+
+        if ($tokens[$classEndIndex]->equalsAny([',', ')'])) { // do the fixing
+            array_pop($classPartTokens);
+            $isInstanceOfVar = (reset($classPartTokens))->isGivenKind(T_VARIABLE);
+            $insertIndex = $testIndex - 1;
+            $newTokens = [];
+
+            foreach ($classPartTokens as $token) {
+                $newTokens[++$insertIndex] = clone $token;
+            }
+
+            if (!$isInstanceOfVar) {
+                $newTokens[++$insertIndex] = new Token([T_DOUBLE_COLON, '::']);
+                $newTokens[++$insertIndex] = new Token([CT::T_CLASS_CONSTANT, 'class']);
+            }
+
+            $newTokens[++$insertIndex] = new Token(',');
+            $newTokens[++$insertIndex] = new Token([T_WHITESPACE, ' ']);
+            $newTokens[++$insertIndex] = clone $tokens[$variableIndex];
+
+            for ($i = $classEndIndex - 1; $i >= $testIndex; --$i) {
+                if (!$tokens[$i]->isComment()) {
+                    $tokens->clearTokenAndMergeSurroundingWhitespace($i);
+                }
+            }
+
+            $tokens->insertSlices($newTokens);
+            $tokens[$assertCall['index']] = new Token([T_STRING, $positive ? 'assertInstanceOf' : 'assertNotInstanceOf']);
+        }
+
+        return true;
+    }
+
     private function fixAssertSameEquals(Tokens $tokens, array $assertCall): void
     {
         // @ $this->/self::assertEquals/Same([$nextIndex])
diff --git a/tests/Fixer/PhpUnit/PhpUnitDedicateAssertFixerTest.php b/tests/Fixer/PhpUnit/PhpUnitDedicateAssertFixerTest.php
index 0fad8e4d8f1..0495a3e0407 100644
--- a/tests/Fixer/PhpUnit/PhpUnitDedicateAssertFixerTest.php
+++ b/tests/Fixer/PhpUnit/PhpUnitDedicateAssertFixerTest.php
@@ -267,6 +267,55 @@ public function provideTestFixCases(): \Generator
             self::generateTest('self::assertStringEndsNotWith($needle, $haystack);'),
             self::generateTest('self::assertFalse(str_ends_with($haystack, $needle));'),
         ];
+
+        yield '$a instanceof class' => [
+            self::generateTest('
+                $this->assertInstanceOf(SomeClass::class, $x);
+                $this->assertInstanceOf(SomeClass::class, $y, $message);
+            '),
+            self::generateTest('
+                $this->assertTrue($x instanceof SomeClass);
+                $this->assertTrue($y instanceof SomeClass, $message);
+            '),
+        ];
+
+        yield '$a instanceof class\a\b' => [
+            self::generateTest('
+                $this->assertInstanceOf(\PhpCsFixer\Tests\Fixtures\Test\AbstractFixerTest\SimpleFixer::class, $ii);
+            '),
+            self::generateTest('
+                $this->assertTrue($ii instanceof \PhpCsFixer\Tests\Fixtures\Test\AbstractFixerTest\SimpleFixer);
+            '),
+        ];
+
+        yield '$a instanceof $b' => [
+            self::generateTest('
+                $this->assertInstanceOf($tty, $abc/* 1 *//* 2 */);
+                $this->assertInstanceOf($oo, $def, $message);
+            '),
+            self::generateTest('
+                $this->assertTrue($abc instanceof /* 1 */$tty /* 2 */);
+                $this->assertTrue($def instanceof $oo, $message);
+            '),
+        ];
+
+        yield 'do not fix instance of' => [
+            self::generateTest('
+                $this->assertTrue($gg instanceof $ijl . "X", $something);
+                $this->assertTrue($ff instanceof $klh . $b(1,2,$message), $noMsg);
+            '),
+        ];
+
+        yield '!$a instanceof class' => [
+            self::generateTest('
+                $this->assertNotInstanceOf(SomeClass::class, $x);
+                $this->assertNotInstanceOf(SomeClass::class, $y, $message);
+            '),
+            self::generateTest('
+                $this->assertTrue(!$x instanceof SomeClass);
+                $this->assertTrue(!$y instanceof SomeClass, $message);
+            '),
+        ];
     }
 
     /**