diff --git a/app/coffee/TikzManager.coffee b/app/coffee/TikzManager.coffee
index cfa1332..5c08f20 100644
--- a/app/coffee/TikzManager.coffee
+++ b/app/coffee/TikzManager.coffee
@@ -22,8 +22,8 @@ module.exports = TikzManager =
 
 	_includesTikz: (resource) ->
 		# check if we are using tikz externalize
-		content = resource.content.slice(0,65536)
-		if content.indexOf("\\tikzexternalize") >= 0
+		content = resource.content?.slice(0,65536)
+		if content?.indexOf("\\tikzexternalize") >= 0
 			return true
 		else
 			return false
diff --git a/test/unit/coffee/TikzManager.coffee b/test/unit/coffee/TikzManager.coffee
index 8174b4a..816b3b1 100644
--- a/test/unit/coffee/TikzManager.coffee
+++ b/test/unit/coffee/TikzManager.coffee
@@ -30,6 +30,12 @@ describe 'TikzManager', ->
 				{ path: 'output.tex' }
 			]).should.equal false
 
+		it "should return false if the file has no content", ->
+			@TikzManager.needsOutputFile("main.tex", [
+				{ path: 'foo.tex' },
+				{ path: 'main.tex' }
+			]).should.equal false
+
 	describe "injectOutputFile", ->
 		beforeEach ->
 			@rootDir = "/mock"