diff --git a/src/classicnoise3D.glsl b/src/classicnoise3D.glsl
index 7ed6d79..778de1e 100644
--- a/src/classicnoise3D.glsl
+++ b/src/classicnoise3D.glsl
@@ -17,6 +17,11 @@ vec3 mod289(vec3 x)
   return x - floor(x * (1.0 / 289.0)) * 289.0;
 }
 
+vec4 mod289(vec4 x)
+{
+  return x - floor(x * (1.0 / 289.0)) * 289.0;
+}
+
 vec4 permute(vec4 x)
 {
   return mod289(((x*34.0)+1.0)*x);