diff --git a/README.md b/README.md
index ca31e78..a54cdb8 100644
--- a/README.md
+++ b/README.md
@@ -44,8 +44,10 @@ interpolation.
 ### lume.pingpong(x)
 Ping-pongs the number `x` between 0 and 1.
 
-### lume.distance(x1, y1, x2, y2)
-Returns the distance between the two points.
+### lume.distance(x1, y1, x2, y2 [, squared])
+Returns the distance between the two points. If `squared` is true then the
+squared distance is returned -- this is faster to calculate and can still be
+used when comparing distances.
 
 ### lume.angle(x1, y1, x2, y2)
 Returns the angle between the two points.
diff --git a/lume.lua b/lume.lua
index c9512ec..aeca0c6 100644
--- a/lume.lua
+++ b/lume.lua
@@ -42,8 +42,9 @@ function lume.pingpong(x)
 end
 
 
-function lume.distance(x1, y1, x2, y2)
-  return math.sqrt((x1 - x2) ^ 2 + (y1 - y2) ^ 2)
+function lume.distance(x1, y1, x2, y2, squared)
+  local s = (x1 - x2) ^ 2 + (y1 - y2) ^ 2
+  return squared and s or math.sqrt(s)
 end