diff --git a/spec/stdlib/cson-spec.coffee b/spec/stdlib/cson-spec.coffee
index bf0aaefcf..361eaf330 100644
--- a/spec/stdlib/cson-spec.coffee
+++ b/spec/stdlib/cson-spec.coffee
@@ -58,6 +58,10 @@ describe "CSON", ->
         expect(CSON.stringify(a: ['b'])).toBe "'a': [\n  'b'\n]"
         expect(CSON.stringify(a: ['b', 4])).toBe "'a': [\n  'b'\n  4\n]"
 
+      describe "when the array has an undefined value", ->
+        it "formats the undefined value as null", ->
+          expect(CSON.stringify(['a', undefined, 'b'])).toBe "[\n  'a'\n  null\n  'b'\n]"
+
     describe "when formatting an object", ->
       describe "when the object is empty", ->
         it "returns the empty string", ->
diff --git a/src/stdlib/cson.coffee b/src/stdlib/cson.coffee
index eab575a11..63158f006 100644
--- a/src/stdlib/cson.coffee
+++ b/src/stdlib/cson.coffee
@@ -28,7 +28,7 @@ module.exports =
         cson += @stringifyBoolean(value)
       else if _.isNumber(value)
         cson += @stringifyNumber(value)
-      else if _.isNull(value)
+      else if _.isNull(value) or value is undefined
         cson += @stringifyNull(value)
       else if _.isArray(value)
         cson += @stringifyArray(value, indentLevel + 2)