diff --git a/HISTORY.md b/HISTORY.md
index 85e34523..579f7577 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -4,6 +4,12 @@ All notable changes to this project will be documented in this file.
 
 ## unreleased
 
+* Fixed
+  * `CycloneDX\Core\Validation\ValidatorInterface::validateString()` and implementations
+    are documented as `non-empty-string`, were undocumented `string` before. (via [#63])
+
+[#63]: https://github.com/CycloneDX/cyclonedx-php-library/pull/63
+
 ## 1.4.0 - 2021-12-20
 
 * Added
diff --git a/src/Core/Validation/ValidatorInterface.php b/src/Core/Validation/ValidatorInterface.php
index fb9898af..34e18903 100644
--- a/src/Core/Validation/ValidatorInterface.php
+++ b/src/Core/Validation/ValidatorInterface.php
@@ -34,5 +34,8 @@ public function __construct(SpecInterface $spec);
 
     public function getSpec(): SpecInterface;
 
+    /**
+     * @psalm-param non-empty-string $string
+     */
     public function validateString(string $string): ?ValidationError;
 }
diff --git a/src/Core/Validation/Validators/JsonValidator.php b/src/Core/Validation/Validators/JsonValidator.php
index 202c0796..0e49fddf 100644
--- a/src/Core/Validation/Validators/JsonValidator.php
+++ b/src/Core/Validation/Validators/JsonValidator.php
@@ -54,6 +54,8 @@ protected static function listSchemaFiles(): array
     }
 
     /**
+     * @psalm-param non-empty-string $string
+     *
      * @throws FailedLoadingSchemaException if schema file unknown or not readable
      * @throws JsonException                if loading the JSON failed
      *
diff --git a/src/Core/Validation/Validators/XmlValidator.php b/src/Core/Validation/Validators/XmlValidator.php
index d6b72b4c..a3222ad9 100644
--- a/src/Core/Validation/Validators/XmlValidator.php
+++ b/src/Core/Validation/Validators/XmlValidator.php
@@ -52,6 +52,8 @@ protected static function listSchemaFiles(): array
     }
 
     /**
+     * @psalm-param non-empty-string $string
+     *
      * @throws FailedLoadingSchemaException if schema file unknown or not readable
      * @throws DOMException                 if loading the DOM failed
      *
@@ -97,6 +99,8 @@ private function validateDomWithSchema(DOMDocument $doc): ?\LibXMLError
     }
 
     /**
+     * @psalm-param non-empty-string $xml
+     *
      * @throws DOMException if loading the DOM failed
      */
     private function loadDomFromXml(string $xml): DOMDocument
diff --git a/tools/psalm/composer.json b/tools/psalm/composer.json
index e638bf4c..7f674072 100644
--- a/tools/psalm/composer.json
+++ b/tools/psalm/composer.json
@@ -4,7 +4,7 @@
     "type": "metapackage",
     "require-dev": {
         "roave/security-advisories": "dev-latest",
-        "vimeo/psalm": "4.18.1"
+        "vimeo/psalm": "4.19.0"
     },
     "prefer-stable": true,
     "config": {