diff --git a/src/builder/balanced/balanced-reducer.js b/src/builder/balanced/balanced-reducer.js
index 12291a43..2bd45cd0 100644
--- a/src/builder/balanced/balanced-reducer.js
+++ b/src/builder/balanced/balanced-reducer.js
@@ -1,6 +1,5 @@
 'use strict'
 
-const assert = require('assert')
 const pull = require('pull-stream')
 const pushable = require('pull-pushable')
 const pullPair = require('pull-pair')
@@ -17,9 +16,12 @@ module.exports = function balancedReduceToRoot (reduce, options) {
       result.end(err)
       return // early
     }
-    assert.equal(roots.length, 1, 'need one root')
-    result.push(roots[0])
-    result.end()
+    if (roots.length === 1) {
+      result.push(roots[0])
+      result.end()
+    } else if (roots.length > 1) {
+      result.end(new Error('expected a maximum of 0 roots and got ' + roots.length))
+    }
   })
 
   function reduceToParents (_chunks, callback) {
diff --git a/src/builder/trickle/trickle-reducer.js b/src/builder/trickle/trickle-reducer.js
index 92f9456f..ebc34753 100644
--- a/src/builder/trickle/trickle-reducer.js
+++ b/src/builder/trickle/trickle-reducer.js
@@ -1,6 +1,5 @@
 'use strict'
 
-const assert = require('assert')
 const pull = require('pull-stream')
 const pushable = require('pull-pushable')
 const batch = require('pull-batch')
@@ -21,13 +20,16 @@ module.exports = function trickleReduceToRoot (reduce, options) {
     trickle(0, -1),
     batch(Infinity),
     pull.asyncMap(reduce),
-    pull.collect((err, nodes) => {
+    pull.collect((err, roots) => {
       if (err) {
         result.end(err)
       } else {
-        assert.equal(nodes.length, 1, 'need one root')
-        result.push(nodes[0])
-        result.end()
+        if (roots.length === 1) {
+          result.push(roots[0])
+          result.end()
+        } else if (roots.length > 1) {
+          result.end(new Error('expected a maximum of 0 roots and got ' + roots.length))
+        }
       }
     })
   )
diff --git a/test/test-importer.js b/test/test-importer.js
index 351208cf..8b072767 100644
--- a/test/test-importer.js
+++ b/test/test-importer.js
@@ -184,6 +184,17 @@ module.exports = (repo) => {
         )
       })
 
+      it('doesn\'t yield anything on empty source', (done) => {
+        pull(
+          pull.empty(),
+          importer(ipldResolver, options),
+          pull.collect((err, nodes) => {
+            expect(err).to.not.exist
+            expect(nodes.length).to.be.eql(0)
+            done()
+          }))
+      })
+
       it('fails on more than one root', (done) => {
         pull(
           pull.values([