diff --git a/.changeset/wise-monkeys-leave.md b/.changeset/wise-monkeys-leave.md
new file mode 100644
index 00000000000..3889323239a
--- /dev/null
+++ b/.changeset/wise-monkeys-leave.md
@@ -0,0 +1,5 @@
+---
+"@smithy/types": patch
+---
+
+Allow lowercase type names for endpoint parameter
diff --git a/packages/types/src/endpoints/RuleSetObject.ts b/packages/types/src/endpoints/RuleSetObject.ts
index 013e466f89a..fac027ecf73 100644
--- a/packages/types/src/endpoints/RuleSetObject.ts
+++ b/packages/types/src/endpoints/RuleSetObject.ts
@@ -6,7 +6,7 @@ export type DeprecatedObject = {
 };
 
 export type ParameterObject = {
-  type: "String" | "Boolean";
+  type: "String" | "string" | "Boolean" | "boolean";
   default?: string | boolean;
   required?: boolean;
   documentation?: string;