diff --git a/index.d.ts b/index.d.ts
index 67ce8ee..577d835 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -350,6 +350,8 @@ export function substitute(type: any, substitutions: any, stack: any): any;
 
 export function sumType(typeParam: any): any;
 
+export function transitivelyGrow(uni: any): any;
+
 export function unify(fType: any, aType: any): any;
 
 export function unifyLL(typeA: any, typeB: any): any;
diff --git a/lib/generics/low_level.js b/lib/generics/low_level.js
index d313060..90a7520 100644
--- a/lib/generics/low_level.js
+++ b/lib/generics/low_level.js
@@ -79,7 +79,7 @@ export const mergeUnifications = (unifA, unifB) => {
   return result;
 };
 
-const transitivelyGrow = (unif) => {
+export const transitivelyGrow = (unif) => {
   let stable = true;
   const result = new Map();
   for (const [symbol, setOfTypes] of unif) {