diff --git a/src/base58.coffee b/src/base58.coffee
index 30b2082..eadb6cd 100644
--- a/src/base58.coffee
+++ b/src/base58.coffee
@@ -4,7 +4,7 @@ class Base58Builder
     @base = @alphabet.length
 
   encode: (num) ->
-    throw new Error('Value passed is not a number.') if typeof num != 'number'
+    throw new Error('Value passed is not an integer.') unless /^\d+$/.test num
     str = ''
     while num >= @base
       mod = num % @base
diff --git a/test/base58_test.coffee b/test/base58_test.coffee
index 6efc829..0dad57f 100644
--- a/test/base58_test.coffee
+++ b/test/base58_test.coffee
@@ -10,9 +10,15 @@ describe 'Base58', ->
       for str, num of examples
         Base58.encode(num).should.eql(str)
 
+    describe 'when passed a float', ->
+      it 'throws an error', ->
+        (-> Base58.encode(3.14)).should
+          .throw('Value passed is not an integer.')
+
     describe 'when passed a non-number value', ->
       it 'throws an error', ->
-        (-> Base58.encode('hi')).should.throw('Value passed is not a number.')
+        (-> Base58.encode('hi')).should
+          .throw('Value passed is not an integer.')
 
   describe '.decode', ->
     it 'decodes Base58 string to number', ->