diff --git a/README.md b/README.md
index bb67601..10e27b6 100644
--- a/README.md
+++ b/README.md
@@ -18,7 +18,7 @@ A strongly typed drop-in replacement for Promises in TypeScript.
 ## Installation
 
 Promise is available from the NPM registry and as a GitHub Package. Whichever
-source you prefer to use, the installation instructions should remain the same.
+source you prefer to use, the installation should remain the same.
 
 ```sh
 # Using NPM
diff --git a/lib/promise.d.ts b/lib/promise.d.ts
index 04c08c1..88523d4 100644
--- a/lib/promise.d.ts
+++ b/lib/promise.d.ts
@@ -89,7 +89,7 @@ declare type AssertRejects<T extends Promise<any, U>, U extends RejectType<V>, V
  * Upgrade a vanilla Promise to a strongly typed Promise while respecting
  * function overloads.
  *
- * Support is provided for functions with four or fewer arguments.
+ * Support is provided for functions with six or fewer overloads.
  *
  * @remarks
  *
@@ -99,6 +99,12 @@ declare type AssertRejects<T extends Promise<any, U>, U extends RejectType<V>, V
  * {@link https://stackoverflow.com/a/64330561/4000053}
  */
 type UpgradePromise<T, E = unknown> =
+  T extends
+    { (...args: infer A1): PromiseLike<infer R1>; (...args: infer A2): PromiseLike<infer R2>; (...args: infer A3): PromiseLike<infer R3>; (...args: infer A4): PromiseLike<infer R4>; (...args: infer A5): PromiseLike<infer R5>; (...args: infer A6): PromiseLike<infer R6>; } ?
+    { (...args: A1): Promise<R1, E>; (...args: A2): Promise<R2, E>; (...args: A3): Promise<R3, E>; (...args: A4): Promise<R4, E>; (...args: A5): Promise<R5, E>; (...args: A6): Promise<R6, E>; } :
+  T extends
+    { (...args: infer A1): PromiseLike<infer R1>; (...args: infer A2): PromiseLike<infer R2>; (...args: infer A3): PromiseLike<infer R3>; (...args: infer A4): PromiseLike<infer R4>; (...args: infer A5): PromiseLike<infer R5>; } ?
+    { (...args: A1): Promise<R1, E>; (...args: A2): Promise<R2, E>; (...args: A3): Promise<R3, E>; (...args: A4): Promise<R4, E>; (...args: A5): Promise<R5, E>; } :
   T extends
     { (...args: infer A1): PromiseLike<infer R1>; (...args: infer A2): PromiseLike<infer R2>; (...args: infer A3): PromiseLike<infer R3>; (...args: infer A4): PromiseLike<infer R4>; } ?
     { (...args: A1): Promise<R1, E>; (...args: A2): Promise<R2, E>; (...args: A3): Promise<R3, E>; (...args: A4): Promise<R4, E>; } :