diff --git a/modules/core/validator.js b/modules/core/validator.js
index 4c2364af7..9926cc86b 100644
--- a/modules/core/validator.js
+++ b/modules/core/validator.js
@@ -3,7 +3,7 @@ import { dispatch as d3_dispatch } from 'd3-dispatch';
 import { coreDifference } from './difference';
 import { geoExtent } from '../geo';
 import { osmEntity } from '../osm';
-import { utilArrayGroupBy, utilRebind } from '../util';
+import { utilArrayGroupBy, utilCallWhenIdle, utilRebind } from '../util';
 import * as Validations from '../validations/index';
 
 
@@ -306,9 +306,11 @@ export function coreValidator(context) {
 
     // re-run validation upon merging fetched data
     context.history().on('merge.validator', function(entities) {
-        if (!entities) return;
-        var ids = entities.map(function(entity) { return entity.id; });
-        validator.validateEntities(ids);
+        utilCallWhenIdle(function() {
+            if (!entities) return;
+            var ids = entities.map(function(entity) { return entity.id; });
+            validator.validateEntities(ids);
+        })();
     });
 
     // // re-run validation on history change (frequent)
diff --git a/modules/util/call_when_idle.js b/modules/util/call_when_idle.js
deleted file mode 100644
index 1b8ae482a..000000000
--- a/modules/util/call_when_idle.js
+++ /dev/null
@@ -1,11 +0,0 @@
-// note the function should be of low priority
-// and should not be returning a value.
-export function utilCallWhenIdle(func, timeout) {
-    return function() {
-        var args = arguments;
-        var that = this;
-        window.requestIdleCallback(function() {
-            func.apply(that, args);
-        }, {timeout: timeout});
-    };
-}
diff --git a/modules/util/idle_worker.js b/modules/util/idle.js
similarity index 59%
rename from modules/util/idle_worker.js
rename to modules/util/idle.js
index 5e75ef324..103e0eded 100644
--- a/modules/util/idle_worker.js
+++ b/modules/util/idle.js
@@ -1,10 +1,32 @@
+// call a single function while idle.
+// note the function should be of low priority
+// and should not be returning a value.
+export function utilCallWhenIdle(func, timeout) {
+    return function() {
+        var args = arguments;
+        var that = this;
+        window.requestIdleCallback(function() {
+            func.apply(that, args);
+        }, { timeout: timeout });
+    };
+}
+
+// process queue while idle
 export function utilIdleWorker(tasks, processor, callback) {
-    var results = [], result;
-    for (var i = 0; i < tasks.length; i++) {
-        result = processor(tasks[i]);
-        if (result) results.push(result);
-    }
-    callback(results);
+
+    // all tasks in single deferral
+    utilCallWhenIdle(function() {
+        var results = [];
+        var result;
+        for (var i = 0; i < tasks.length; i++) {
+            result = processor(tasks[i]);
+            if (result) results.push(result);
+        }
+        callback(results);
+    })();
+
+    // alternatively, each task deferred in its own callback
+    // seems to not work because it
 
     // var processed = [];
     // var currentPos = 0;
@@ -36,7 +58,7 @@ window.requestIdleCallback =
     window.requestIdleCallback ||
     function(cb) {
         var start = Date.now();
-        return setTimeout(function() {
+        return window.setTimeout(function() {
             cb({
                 didTimeout: false,
                 timeRemaining: function() {
@@ -49,5 +71,5 @@ window.requestIdleCallback =
 window.cancelIdleCallback =
     window.cancelIdleCallback ||
     function(id) {
-        clearTimeout(id);
+        window.clearTimeout(id);
     };
diff --git a/modules/util/index.js b/modules/util/index.js
index 3ca8460cb..b7d51e668 100644
--- a/modules/util/index.js
+++ b/modules/util/index.js
@@ -8,7 +8,7 @@ export { utilArrayUniq } from './array';
 export { utilArrayUniqBy } from './array';
 
 export { utilAsyncMap } from './util';
-export { utilCallWhenIdle } from './call_when_idle';
+export { utilCallWhenIdle } from './idle';
 export { utilCleanTags } from './clean_tags';
 export { utilDisplayName } from './util';
 export { utilDisplayNameForPath } from './util';
@@ -25,7 +25,7 @@ export { utilGetAllNodes } from './util';
 export { utilGetSetValue } from './get_set_value';
 export { utilHashcode } from './util';
 export { utilHighlightEntities } from './util';
-export { utilIdleWorker } from './idle_worker';
+export { utilIdleWorker } from './idle';
 export { utilKeybinding } from './keybinding';
 export { utilNoAuto } from './util';
 export { utilObjectOmit } from './object';