diff --git a/libImaging/Antialias.c b/libImaging/Antialias.c
index d413fbb6a..e608ec8df 100644
--- a/libImaging/Antialias.c
+++ b/libImaging/Antialias.c
@@ -64,16 +64,14 @@ static struct filter BILINEAR = { bilinear_filter, 1.0 };
 
 static inline float bicubic_filter(float x)
 {
-    /* FIXME: double-check this algorithm */
-    /* FIXME: for best results, "a" should be -0.5 to -1.0, but we'll
-       set it to zero for now, to match the 1.1 magnifying filter */
-#define a 0.0
+    /* http://en.wikipedia.org/wiki/Bicubic_interpolation#Bicubic_convolution_algorithm */
+#define a -1.0
     if (x < 0.0)
         x = -x;
     if (x < 1.0)
-        return (((a + 2.0) * x) - (a + 3.0)) * x*x + 1;
+        return ((a + 2.0) * x - (a + 3.0)) * x*x + 1;
     if (x < 2.0)
-        return (((a * x) - 5*a) * x + 8) * x - 4*a;
+        return (((x - 5) * x + 8) * x - 4) * a;
     return 0.0;
 #undef a
 }