diff --git a/packages/openapi-typescript/src/transform/schema-object.ts b/packages/openapi-typescript/src/transform/schema-object.ts
index baa143933..7219664df 100644
--- a/packages/openapi-typescript/src/transform/schema-object.ts
+++ b/packages/openapi-typescript/src/transform/schema-object.ts
@@ -322,7 +322,7 @@ function transformSchemaObjectCore(schemaObject: SchemaObject, options: Transfor
       }
       // standard array type
       else if (schemaObject.items) {
-        if ("type" in schemaObject.items && schemaObject.items.type === "array") {
+        if (hasKey(schemaObject.items, "type") && schemaObject.items.type === "array") {
           itemType = ts.factory.createArrayTypeNode(transformSchemaObject(schemaObject.items, options));
         } else {
           itemType = transformSchemaObject(schemaObject.items, options);
@@ -579,3 +579,13 @@ function transformSchemaObjectCore(schemaObject: SchemaObject, options: Transfor
 
   return coreObjectType.length ? ts.factory.createTypeLiteralNode(coreObjectType) : undefined;
 }
+
+/**
+ * Check if an object has a key
+ * @param possibleObject - The object to check
+ * @param key - The key to check for
+ * @returns True if the object has the key, false otherwise
+ */
+function hasKey<K extends string>(possibleObject: unknown, key: K): possibleObject is { [key in K]: unknown } {
+  return typeof possibleObject === "object" && possibleObject !== null && key in possibleObject;
+}
diff --git a/packages/openapi-typescript/test/transform/schema-object/array.test.ts b/packages/openapi-typescript/test/transform/schema-object/array.test.ts
index 37d468766..fe3e53358 100644
--- a/packages/openapi-typescript/test/transform/schema-object/array.test.ts
+++ b/packages/openapi-typescript/test/transform/schema-object/array.test.ts
@@ -18,6 +18,14 @@ describe("transformSchemaObject > array", () => {
         // options: DEFAULT_OPTIONS,
       },
     ],
+    // Prevents: "TypeError: Cannot use 'in' operator to search for 'type' in true"
+    [
+      "boolean items",
+      {
+        given: { type: "array", items: true },
+        want: "unknown[]",
+      },
+    ],
     [
       "tuple > tuple items",
       {