diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/OpenAPINormalizer.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/OpenAPINormalizer.java
index d3317375321b..1b1dd2c6538e 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/OpenAPINormalizer.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/OpenAPINormalizer.java
@@ -1280,6 +1280,9 @@ private Schema processNormalize31Spec(Schema schema, Set<Schema> visitedSchemas)
                         Schema updatedItems = normalizeSchema(schema.getItems(), visitedSchemas);
                         as.setItems(updatedItems);
                     }
+                } else {
+                    // when items is not defined, default to any type
+                    as.setItems(new Schema());
                 }
 
                 return as;
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/OpenAPINormalizerTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/OpenAPINormalizerTest.java
index 70c04397e233..3537cc5b8974 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/OpenAPINormalizerTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/OpenAPINormalizerTest.java
@@ -600,6 +600,11 @@ public void testOpenAPINormalizerProcessingArraySchema31Spec() {
         assertEquals(((Schema) schema5.getProperties().get("arrayOfStrings")).getItems().getType(), null);
         assertEquals(((Schema) schema5.getProperties().get("arrayOfStrings")).getItems().getTypes().contains("string"), true);
 
+        Schema schema7 = openAPI.getComponents().getSchemas().get("ArrayWithPrefixItems");
+        assertEquals(((Schema) schema7.getProperties().get("with_prefixitems")).getItems(), null);
+        assertNotEquals(((Schema) schema7.getProperties().get("with_prefixitems")).getPrefixItems(), null);
+        assertEquals(((Schema) schema7.getProperties().get("without_items")).getItems(), null);
+
         Map<String, String> inputRules = Map.of("NORMALIZE_31SPEC", "true");
         OpenAPINormalizer openAPINormalizer = new OpenAPINormalizer(openAPI, inputRules);
         openAPINormalizer.normalize();
@@ -622,6 +627,11 @@ public void testOpenAPINormalizerProcessingArraySchema31Spec() {
         assertEquals(((Schema) schema6.getProperties().get("arrayOfStrings")).getItems().getTypes().contains("string"), true);
         assertEquals(((Schema) schema6.getProperties().get("arrayOfStrings")).getItems().getType(), "string");
         assertEquals(((Schema) schema6.getProperties().get("arrayOfStrings")).getType(), "array");
+
+        Schema schema8 = openAPI.getComponents().getSchemas().get("ArrayWithPrefixItems");
+        assertNotEquals(((Schema) schema8.getProperties().get("with_prefixitems")).getItems(), null);
+        assertEquals(((Schema) schema8.getProperties().get("with_prefixitems")).getPrefixItems(), null);
+        assertNotEquals(((Schema) schema8.getProperties().get("without_items")).getItems(), null);
     }
 
     @Test
diff --git a/modules/openapi-generator/src/test/resources/3_1/issue_18291.yaml b/modules/openapi-generator/src/test/resources/3_1/issue_18291.yaml
index 8f5b9db4e1a8..8ea8a90357f6 100644
--- a/modules/openapi-generator/src/test/resources/3_1/issue_18291.yaml
+++ b/modules/openapi-generator/src/test/resources/3_1/issue_18291.yaml
@@ -30,7 +30,20 @@ components:
           type: array
           items:
             type: string
-
     Bar:
       allOf:
-        - $ref: '#/components/schemas/Foo'
\ No newline at end of file
+        - $ref: '#/components/schemas/Foo'
+    ArrayWithPrefixItems:
+      type: object
+      properties:
+        with_prefixitems:
+          type: array
+          prefixItems:
+            - type: number
+              title: Longitude
+            - type: number
+              title: Latitude
+          maxItems: 2
+          minItems: 2
+        without_items:
+          type: array