diff --git a/src/Rules/PHPUnit/CoversHelper.php b/src/Rules/PHPUnit/CoversHelper.php
index a96257f..792fcc1 100644
--- a/src/Rules/PHPUnit/CoversHelper.php
+++ b/src/Rules/PHPUnit/CoversHelper.php
@@ -105,11 +105,17 @@ public function processCovers(
 				return $errors;
 			}
 
-			$errors[] = RuleErrorBuilder::message(sprintf(
+			$error = RuleErrorBuilder::message(sprintf(
 				'@covers value %s references an invalid %s.',
 				$fullName,
 				$isMethod ? 'method' : 'class or function'
-			))->build();
+			));
+
+			if (strpos($className, '\\') === false) {
+				$error->tip('The @covers annotation requires a fully qualified name.');
+			}
+
+			$errors[] = $error->build();
 		}
 		return $errors;
 	}
diff --git a/tests/Rules/PHPUnit/ClassCoversExistsRuleTest.php b/tests/Rules/PHPUnit/ClassCoversExistsRuleTest.php
index 7b84b50..32806ed 100644
--- a/tests/Rules/PHPUnit/ClassCoversExistsRuleTest.php
+++ b/tests/Rules/PHPUnit/ClassCoversExistsRuleTest.php
@@ -40,6 +40,11 @@ public function testRule(): void
 				'@covers value does not specify anything.',
 				43,
 			],
+			[
+				'@covers value NotFullyQualified references an invalid class or function.',
+				50,
+				'The @covers annotation requires a fully qualified name.',
+			],
 		]);
 	}
 
diff --git a/tests/Rules/PHPUnit/data/class-coverage.php b/tests/Rules/PHPUnit/data/class-coverage.php
index a5ddd18..35af204 100644
--- a/tests/Rules/PHPUnit/data/class-coverage.php
+++ b/tests/Rules/PHPUnit/data/class-coverage.php
@@ -43,3 +43,10 @@ function testable(): void
 class CoversNothing extends \PHPUnit\Framework\TestCase
 {
 }
+
+/**
+ * @covers NotFullyQualified
+ */
+class CoversNotFullyQualified extends \PHPUnit\Framework\TestCase
+{
+}