diff --git a/CHANGELOG.md b/CHANGELOG.md
index e39699b8..65250de3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -34,7 +34,8 @@ Please also have a look at our
 - Use more native type declarations and strict mode
   (#641, #772, #774, #778, #804, #841, #873, #875, #891, #922, #923, #933, #958,
   #964, #967, #1000, #1044, #1134, #1136, #1137, #1139, #1140, #1141, #1145,
-  #1162, #1163, #1166, #1172, #1174, #1178, #1179, #1181, #1183, #1184, #1186)
+  #1162, #1163, #1166, #1172, #1174, #1178, #1179, #1181, #1183, #1184, #1186,
+  #1187)
 - Add visibility to all class/interface constants (#469)
 
 ### Deprecated
diff --git a/config/phpstan-baseline.neon b/config/phpstan-baseline.neon
index 889cc859..722454ba 100644
--- a/config/phpstan-baseline.neon
+++ b/config/phpstan-baseline.neon
@@ -30,18 +30,6 @@ parameters:
 			count: 1
 			path: ../src/CSSList/Document.php
 
-		-
-			message: '#^Cannot call method render\(\) on string\.$#'
-			identifier: method.nonObject
-			count: 1
-			path: ../src/Property/CSSNamespace.php
-
-		-
-			message: '#^Only booleans are allowed in an if condition, string given\.$#'
-			identifier: if.condNotBoolean
-			count: 1
-			path: ../src/Property/CSSNamespace.php
-
 		-
 			message: '#^Only booleans are allowed in an if condition, Sabberworm\\CSS\\Value\\RuleValueList\|string\|null given\.$#'
 			identifier: if.condNotBoolean
diff --git a/src/Property/CSSNamespace.php b/src/Property/CSSNamespace.php
index 75336249..5b174861 100644
--- a/src/Property/CSSNamespace.php
+++ b/src/Property/CSSNamespace.php
@@ -6,6 +6,8 @@
 
 use Sabberworm\CSS\Comment\Comment;
 use Sabberworm\CSS\OutputFormat;
+use Sabberworm\CSS\Value\CSSString;
+use Sabberworm\CSS\Value\URL;
 
 /**
  * `CSSNamespace` represents an `@namespace` rule.
@@ -13,12 +15,12 @@
 class CSSNamespace implements AtRule
 {
     /**
-     * @var string
+     * @var CSSString|URL
      */
     private $url;
 
     /**
-     * @var string
+     * @var string|null
      */
     private $prefix;
 
@@ -35,11 +37,10 @@ class CSSNamespace implements AtRule
     protected $comments = [];
 
     /**
-     * @param string $url
-     * @param string|null $prefix
+     * @param CSSString|URL $url
      * @param int<0, max> $lineNumber
      */
-    public function __construct($url, $prefix = null, int $lineNumber = 0)
+    public function __construct($url, ?string $prefix = null, int $lineNumber = 0)
     {
         $this->url = $url;
         $this->prefix = $prefix;
@@ -61,33 +62,27 @@ public function render(OutputFormat $outputFormat): string
     }
 
     /**
-     * @return string
+     * @return CSSString|URL
      */
     public function getUrl()
     {
         return $this->url;
     }
 
-    /**
-     * @return string|null
-     */
-    public function getPrefix()
+    public function getPrefix(): ?string
     {
         return $this->prefix;
     }
 
     /**
-     * @param string $url
+     * @param CSSString|URL $url
      */
     public function setUrl($url): void
     {
         $this->url = $url;
     }
 
-    /**
-     * @param string $prefix
-     */
-    public function setPrefix($prefix): void
+    public function setPrefix(string $prefix): void
     {
         $this->prefix = $prefix;
     }
@@ -101,12 +96,12 @@ public function atRuleName(): string
     }
 
     /**
-     * @return array<int, string>
+     * @return array{0: CSSString|URL|non-empty-string, 1?: CSSString|URL}
      */
     public function atRuleArgs(): array
     {
         $result = [$this->url];
-        if ($this->prefix) {
+        if (\is_string($this->prefix) && $this->prefix !== '') {
             \array_unshift($result, $this->prefix);
         }
         return $result;