diff --git a/test/index.js b/test/index.js
index 0c6b8f3..25e2306 100644
--- a/test/index.js
+++ b/test/index.js
@@ -11,6 +11,16 @@ describe('convert', function () {
     assert.equal(Units.convert('1', 'finney', 'eth'), '0.001')
     assert.equal(Units.convert('20', 'gwei', 'eth'), '0.00000002')
   })
+  it('should fail on invalid input units', function () {
+    assert.throws(function () {
+      Units.convert('1', 'random', 'wei')
+    }, /^Error: Unsupported input unit$/)
+  })
+  it('should fail on invalid output units', function () {
+    assert.throws(function () {
+      Units.convert('1', 'wei', 'random')
+    }, /^Error: Unsupported output unit$/)
+  })
 })
 
 describe('lazyConvert', function () {
@@ -23,6 +33,15 @@ describe('lazyConvert', function () {
     assert.equal(Units.lazyConvert('1 finney', 'eth'), '0.001 eth')
     assert.equal(Units.lazyConvert('20 gwei', 'eth'), '0.00000002 eth')
   })
+  it('should fail on invalid input', function () {
+    assert.throws(function () {
+      Units.lazyConvert('1')
+    }, /^Error: Invalid input$/)
+
+    assert.throws(function () {
+      Units.lazyConvert('1 eth wei')
+    }, /^Error: Invalid input$/)
+  })
 })
 
 describe('units export', function () {