diff --git a/src/Type/PHPUnit/Assert/AssertFunctionTypeSpecifyingExtension.php b/src/Type/PHPUnit/Assert/AssertFunctionTypeSpecifyingExtension.php
index 6a684d3..d4ec8fb 100644
--- a/src/Type/PHPUnit/Assert/AssertFunctionTypeSpecifyingExtension.php
+++ b/src/Type/PHPUnit/Assert/AssertFunctionTypeSpecifyingExtension.php
@@ -29,7 +29,7 @@ public function isFunctionSupported(
 	): bool
 	{
 		return AssertTypeSpecifyingExtensionHelper::isSupported(
-			$functionReflection->getName(),
+			$this->trimName($functionReflection->getName()),
 			$node->args
 		);
 	}
@@ -44,9 +44,19 @@ public function specifyTypes(
 		return AssertTypeSpecifyingExtensionHelper::specifyTypes(
 			$this->typeSpecifier,
 			$scope,
-			$functionReflection->getName(),
+			$this->trimName($functionReflection->getName()),
 			$node->args
 		);
 	}
 
+	private function trimName(string $functionName): string
+	{
+		$prefix = 'PHPUnit\\Framework\\';
+		if (strpos($functionName, $prefix) === 0) {
+			return substr($functionName, strlen($prefix));
+		}
+
+		return $functionName;
+	}
+
 }
diff --git a/tests/Type/PHPUnit/AssertFunctionTypeSpecifyingExtensionTest.php b/tests/Type/PHPUnit/AssertFunctionTypeSpecifyingExtensionTest.php
new file mode 100644
index 0000000..e1984cf
--- /dev/null
+++ b/tests/Type/PHPUnit/AssertFunctionTypeSpecifyingExtensionTest.php
@@ -0,0 +1,36 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\PHPUnit;
+
+use PHPStan\Testing\TypeInferenceTestCase;
+
+class AssertFunctionTypeSpecifyingExtensionTest extends TypeInferenceTestCase
+{
+
+	/** @return mixed[] */
+	public function dataFileAsserts(): iterable
+	{
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/assert-function.php');
+	}
+
+	/**
+	 * @dataProvider dataFileAsserts
+	 * @param string $assertType
+	 * @param string $file
+	 * @param mixed ...$args
+	 */
+	public function testFileAsserts(
+		string $assertType,
+		string $file,
+		...$args
+	): void
+	{
+		$this->assertFileAsserts($assertType, $file, ...$args);
+	}
+
+	public static function getAdditionalConfigFiles(): array
+	{
+		return [__DIR__ . '/../../../extension.neon'];
+	}
+
+}
diff --git a/tests/Type/PHPUnit/data/assert-function.php b/tests/Type/PHPUnit/data/assert-function.php
new file mode 100644
index 0000000..5c1cc96
--- /dev/null
+++ b/tests/Type/PHPUnit/data/assert-function.php
@@ -0,0 +1,20 @@
+<?php
+
+namespace AssertFunction;
+
+use function PHPStan\Testing\assertType;
+use function PHPUnit\Framework\assertInstanceOf;
+
+class Foo
+{
+
+	/**
+	 * @param object $o
+	 */
+	public function doFoo($o): void
+	{
+		assertInstanceOf(self::class, $o);
+		assertType(self::class, $o);
+	}
+
+}