diff --git a/src/basics.cc b/src/basics.cc
index 46361bc..fc4ddd7 100644
--- a/src/basics.cc
+++ b/src/basics.cc
@@ -299,7 +299,7 @@ Ray::Ray(Vector3 o, Vector3 d)
  * Compute and return the point given by parameterizing this Ray by time t.
  */
 Vector3
-Ray::parameterize(const float t)
+Ray::parameterize(const Double& t)
     const
 {
     return origin + t * direction;
diff --git a/src/basics.h b/src/basics.h
index 1ef6f2a..d84c197 100644
--- a/src/basics.h
+++ b/src/basics.h
@@ -124,7 +124,7 @@ struct Ray
     Ray();
     Ray(Vector3 o, Vector3 d);
 
-    Vector3 parameterize(const float t) const;
+    Vector3 parameterize(const Double& t) const;
 
     Vector3 origin, direction;
 };