diff --git a/src/index.js b/src/index.js
index 73a89ee..21741a4 100644
--- a/src/index.js
+++ b/src/index.js
@@ -55,9 +55,10 @@ function tileReduce(options) {
 
   if (output) output.setMaxListeners(0);
   var mapOptions = options.mapOptions || {};
+  var requireData = options.requireData || 'all';
 
   for (var i = 0; i < maxWorkers; i++) {
-    var worker = fork(path.join(__dirname, 'worker.js'), [options.map, JSON.stringify(options.sources), JSON.stringify(mapOptions)], {silent: true});
+    var worker = fork(path.join(__dirname, 'worker.js'), [options.map, JSON.stringify(options.sources), JSON.stringify(mapOptions), requireData], {silent: true});
     worker.stdout.pipe(binarysplit('\x1e')).pipe(output);
     worker.stderr.pipe(process.stderr);
     worker.on('message', handleMessage);
diff --git a/src/worker.js b/src/worker.js
index aab08f4..e387e7f 100644
--- a/src/worker.js
+++ b/src/worker.js
@@ -8,6 +8,7 @@ var isOldNode = process.versions.node.split('.')[0] < 4;
 
 global.mapOptions = JSON.parse(process.argv[4]);
 var map = require(process.argv[2]);
+var requireData = process.argv[5];
 
 JSON.parse(process.argv[3]).forEach(function(source) {
   q.defer(loadSource, source);
@@ -42,14 +43,24 @@ function processTile(tile, callback) {
     if (err) throw err;
 
     var data = {};
+    var hasData = false;
     for (var i = 0; i < results.length; i++) {
       data[sources[i].name] = results[i];
       if (!results[i]) {
-        callback();
-        process.send({reduce: true});
-        return;
+        if (requireData === 'all') {
+          callback();
+          process.send({reduce: true});
+          return;
+        }
+      } else {
+        hasData = true;
       }
     }
+    if (requireData === 'any' && !hasData) {
+      callback();
+      process.send({reduce: true});
+      return;
+    }
 
     var writeQueue = queue(1);