diff --git a/.changeset/hungry-files-scream.md b/.changeset/hungry-files-scream.md
new file mode 100644
index 0000000000..18a0e39c01
--- /dev/null
+++ b/.changeset/hungry-files-scream.md
@@ -0,0 +1,6 @@
+---
+"@redocly/openapi-core": patch
+"@redocly/cli": patch
+---
+
+Removed `additionalItems` from OAS 3.0.x typings. This keyword is not supported by the specification
diff --git a/packages/core/src/types/oas3.ts b/packages/core/src/types/oas3.ts
index e51ece0dc3..647e3acf86 100755
--- a/packages/core/src/types/oas3.ts
+++ b/packages/core/src/types/oas3.ts
@@ -346,13 +346,6 @@ const Schema: NodeType = {
         return 'Schema';
       }
     },
-    additionalItems: (value: any) => {
-      if (typeof value === 'boolean') {
-        return { type: 'boolean' };
-      } else {
-        return 'Schema';
-      }
-    },
     additionalProperties: (value: any) => {
       if (typeof value === 'boolean') {
         return { type: 'boolean' };