diff --git a/.github/workflows/continuous_integration.yml b/.github/workflows/continuous_integration.yml
index 07b6da2a08..2fc5c5abd9 100644
--- a/.github/workflows/continuous_integration.yml
+++ b/.github/workflows/continuous_integration.yml
@@ -18,7 +18,7 @@ jobs:
     strategy:
       matrix:
         install-args: ['', '--prefer-lowest']
-        php-version: ['8.1', '8.2', '8.3', '8.4']
+        php-version: ['8.1', '8.2', '8.3', '8.4', '8.5']
       fail-fast: false
 
     steps:
diff --git a/phpstan.neon b/phpstan.neon
index 11a355ed6b..47466309f5 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -39,3 +39,9 @@ parameters:
            path : src/Types/ID.php
         -
            identifier: missingType.generics
+        -
+           message: '#^Possibly invalid array key type string\|null\.$#'
+           path: src/FieldsBuilder.php
+        -
+           message: '#^Possibly invalid array key type string\|null\.$#'
+           path: src/Mappers/GlobTypeMapperCache.php
diff --git a/src/Mappers/Root/IteratorTypeMapper.php b/src/Mappers/Root/IteratorTypeMapper.php
index 767f0489f6..ae5881b5d0 100644
--- a/src/Mappers/Root/IteratorTypeMapper.php
+++ b/src/Mappers/Root/IteratorTypeMapper.php
@@ -229,7 +229,9 @@ private function splitIteratorFromOtherTypes(array &$types): Type|null
         }
 
         // One of the classes in the compound is an iterator. Let's remove it from the list and let's test all other values as potential subTypes.
-        unset($types[$key]);
+        if ($key !== null) {
+            unset($types[$key]);
+        }
 
         return $iteratorType;
     }