diff --git a/Swift/BlurHashDecode.swift b/Swift/BlurHashDecode.swift
index 7fe3b398..dd06fd96 100644
--- a/Swift/BlurHashDecode.swift
+++ b/Swift/BlurHashDecode.swift
@@ -38,7 +38,7 @@ extension UIImage {
 
                 for j in 0 ..< numY {
                     for i in 0 ..< numX {
-                        let basis = cos(Float.pi * Float(x) * Float(i) / Float(width)) * cos(Float.pi * Float(y) * Float(j) / Float(height))
+                        let basis = cos(Float.pi * Float(x) * Float(i) / Float(width - 1)) * cos(Float.pi * Float(y) * Float(j) / Float(height - 1))
                         let colour = colours[i + j * numX]
                         r += colour.0 * basis
                         g += colour.1 * basis