diff --git a/.changeset/swift-garlics-notice.md b/.changeset/swift-garlics-notice.md
new file mode 100644
index 00000000000..8b1afdc2887
--- /dev/null
+++ b/.changeset/swift-garlics-notice.md
@@ -0,0 +1,5 @@
+---
+"@smithy/core": patch
+---
+
+set explicit return type for cbor alloc
diff --git a/packages/core/src/submodules/cbor/cbor-types.ts b/packages/core/src/submodules/cbor/cbor-types.ts
index cef352d394d..f0efb94dc06 100644
--- a/packages/core/src/submodules/cbor/cbor-types.ts
+++ b/packages/core/src/submodules/cbor/cbor-types.ts
@@ -64,7 +64,7 @@ export const extendedFloat64 = 27; // 0b11011
 
 export const minorIndefinite = 31; // 0b11111
 
-export function alloc(size: number) {
+export function alloc(size: number): Uint8Array {
   return typeof Buffer !== "undefined" ? Buffer.alloc(size) : new Uint8Array(size);
 }