diff --git a/libvips/conversion/scale.c b/libvips/conversion/scale.c
index bc74fe78..9f206e88 100644
--- a/libvips/conversion/scale.c
+++ b/libvips/conversion/scale.c
@@ -54,6 +54,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <math.h>
 
 #include <vips/vips.h>