diff --git a/setup.py b/setup.py
index 1090d0b..a18b21f 100644
--- a/setup.py
+++ b/setup.py
@@ -5,5 +5,9 @@ import Cython.Compiler.Options
 Cython.Compiler.Options.annotate = True
 
 setup(
-    ext_modules=cythonize(["dither.pyx"], annotate=True)
+    ext_modules=cythonize(
+        ["dither.pyx"],
+        annotate=True,
+        compiler_directives={'language_level' : "3"}
+    )
 )