diff --git a/plug-ins/common/sphere-designer.c b/plug-ins/common/sphere-designer.c
index f9bf8edd9d..967f625296 100644
--- a/plug-ins/common/sphere-designer.c
+++ b/plug-ins/common/sphere-designer.c
@@ -2018,7 +2018,7 @@ loadit (const gchar * fn)
 
   s.com.numtexture = 0;
 
-  snprintf (fmt_str, sizeof (fmt_str), "%%d %%d %%%ds", sizeof (endbuf) - 1);
+  snprintf (fmt_str, sizeof (fmt_str), "%%d %%d %%%zus", sizeof (endbuf) - 1);
 
   while (!feof (f))
     {