diff --git a/psalm-baseline.xml b/psalm-baseline.xml
index 6b51ada..772444d 100644
--- a/psalm-baseline.xml
+++ b/psalm-baseline.xml
@@ -106,7 +106,6 @@
       <code><![CDATA[\InteractionDesignFoundation\GeoIP\Contracts\ServiceInterface]]></code>
     </MoreSpecificReturnType>
     <PossiblyNullArgument>
-      <code><![CDATA[$ip]]></code>
       <code><![CDATA[$location->iso_code]]></code>
       <code><![CDATA[$this->currencies]]></code>
     </PossiblyNullArgument>
diff --git a/src/GeoIP.php b/src/GeoIP.php
index cbfa223..83bd00a 100644
--- a/src/GeoIP.php
+++ b/src/GeoIP.php
@@ -269,9 +269,14 @@ private function isValid($ip): bool
      * @param string|null $ip
      *
      * @return bool
+     * @psalm-assert-if-true string $ip
      */
-    private function shouldCache(Location $location, $ip = null): bool
+    private function shouldCache(Location $location, ?string $ip = null): bool
     {
+        if ($ip === null) {
+            return false;
+        }
+
         if ($location->default === true || $location->cached === true) {
             return false;
         }