diff --git a/src/data/feature_index.js b/src/data/feature_index.js
index c16eaf186d7..a47ce11d44d 100644
--- a/src/data/feature_index.js
+++ b/src/data/feature_index.js
@@ -11,7 +11,7 @@ import vt from '@mapbox/vector-tile';
 import Protobuf from 'pbf';
 import GeoJSONFeature from '../util/vectortile_to_geojson';
 import { arraysIntersect } from '../util/util';
-import deriveIntegerId from '../util/derive_integer_id';
+import { setIntegerId } from '../util/integer_id';
 import { OverscaledTileID } from '../source/tile_id';
 import { register } from '../util/web_worker_transfer';
 import EvaluationParameters from '../style/evaluation_parameters';
@@ -202,7 +202,7 @@ class FeatureIndex {
             }
 
             if (this.deriveIntegerId) {
-                deriveIntegerId(feature, this.deriveIntegerId);
+                setIntegerId(feature, this.deriveIntegerId);
             }
 
             const geojsonFeature = new GeoJSONFeature(feature, this.z, this.x, this.y);
diff --git a/src/source/worker_tile.js b/src/source/worker_tile.js
index c10e7b43d2b..a3e11b4da4a 100644
--- a/src/source/worker_tile.js
+++ b/src/source/worker_tile.js
@@ -10,7 +10,7 @@ import LineBucket from '../data/bucket/line_bucket';
 import FillBucket from '../data/bucket/fill_bucket';
 import FillExtrusionBucket from '../data/bucket/fill_extrusion_bucket';
 import { warnOnce, mapObject, values } from '../util/util';
-import deriveIntegerId from '../util/derive_integer_id';
+import { setIntegerId } from '../util/integer_id';
 import assert from 'assert';
 import ImageAtlas from '../render/image_atlas';
 import GlyphAtlas from '../render/glyph_atlas';
@@ -99,7 +99,7 @@ class WorkerTile {
             for (let index = 0; index < sourceLayer.length; index++) {
                 const feature = sourceLayer.feature(index);
                 if (this.deriveIntegerId) {
-                    deriveIntegerId(feature, this.deriveIntegerId);
+                    setIntegerId(feature, this.deriveIntegerId);
                 }
                 features.push({ feature, index, sourceLayerIndex });
             }
diff --git a/src/util/derive_integer_id.js b/src/util/derive_integer_id.js
deleted file mode 100644
index 594bf697f55..00000000000
--- a/src/util/derive_integer_id.js
+++ /dev/null
@@ -1,14 +0,0 @@
-// @flow
-
-import murmur3 from 'murmurhash-js';
-
-export default function deriveIntegerId(feature: VectorTileFeature, key: string) {
-    const value = feature.properties[key];
-    if (value === undefined) return;
-
-    if (typeof value === 'number' && value % 1 === 0) {
-        feature.id = value;
-    } else {
-        feature.id = murmur3(String(value));
-    }
-}
diff --git a/src/util/integer_id.js b/src/util/integer_id.js
new file mode 100644
index 00000000000..451e058a279
--- /dev/null
+++ b/src/util/integer_id.js
@@ -0,0 +1,18 @@
+// @flow
+
+import murmur3 from 'murmurhash-js';
+
+export function setIntegerId(feature: VectorTileFeature, key: string) {
+    const value = feature.properties[key];
+    if (value !== undefined) {
+        feature.id = getIntegerId(value);
+    }
+}
+
+export function getIntegerId(value: mixed) {
+    const numValue = +value;
+    if (!isNaN(numValue) && numValue % 1 === 0) {
+        return numValue;
+    }
+    return murmur3(String(value));
+}