diff --git a/src/mol-data/int/impl/interval.ts b/src/mol-data/int/impl/interval.ts
index 4576342994f452081397317f33c2ea14636de720..e4c7ed01c2256eb5dacafb7eb0c171af2c45ffef 100644
--- a/src/mol-data/int/impl/interval.ts
+++ b/src/mol-data/int/impl/interval.ts
@@ -16,7 +16,7 @@ export const start = Tuple.fst;
 export const end = Tuple.snd;
 export const min = Tuple.fst;
 export function max(i: Tuple) { return Tuple.snd(i) - 1; }
-export function size(i: Tuple) { return Tuple.snd(i) - Tuple.fst(i); }
+export const size = Tuple.diff;
 export const hashCode = Tuple.hashCode;
 export const toString = Tuple.toString;