diff --git a/funcs/fimg-png.c b/funcs/fimg-png.c
index 0eede41e..072a0814 100644
--- a/funcs/fimg-png.c
+++ b/funcs/fimg-png.c
@@ -201,7 +201,8 @@ if (NULL==bytes) {
    /* compute max value */
 maximum = (double)fimg_get_maxvalue(src);
 fk = maximum / 255.0;
-if (verbosity > 1) fprintf(stderr, "max val %g fk %g\n", maximum, fk);
+if (verbosity > 1)
+	fprintf(stderr, "%s: max val %g fk %g\n", __func__, maximum, fk);
    /* massage des pixels */
 bptr = bytes;
 for (idx=0; idx<sz; idx++) {