diff --git a/example-application/elm.json b/example-application/elm.json
index 79f1d61f..bb36ba29 100644
--- a/example-application/elm.json
+++ b/example-application/elm.json
@@ -1,7 +1,8 @@
 {
     "type": "application",
     "source-directories": [
-        "src"
+        "src",
+        "tests"
     ],
     "elm-version": "0.19.1",
     "dependencies": {
diff --git a/lib/Project.js b/lib/Project.js
index ff37529d..1e15ae0b 100644
--- a/lib/Project.js
+++ b/lib/Project.js
@@ -39,9 +39,15 @@ function init(
   const projectSourceDirs =
     elmJson.type === 'package' ? ['src'] : elmJson['source-directories'];
 
-  const testsSourceDirs /*: Array<string> */ = projectSourceDirs
-    .map((src) => path.resolve(rootDir, src))
-    .concat(shouldAddTestsDirAsSource ? [testsDir] : []);
+  const resolvedSourceDirs = projectSourceDirs.map((src) =>
+    path.resolve(rootDir, src)
+  );
+
+  const testsSourceDirs = resolvedSourceDirs.includes(testsDir)
+    ? resolvedSourceDirs
+    : shouldAddTestsDirAsSource
+    ? resolvedSourceDirs.concat([testsDir])
+    : resolvedSourceDirs;
 
   const generatedCodeDir = path.join(
     rootDir,