diff --git a/fvn_fnlib/ztan.f b/fvn_fnlib/ztan.f
index 72ad2ab..6da169c 100644
--- a/fvn_fnlib/ztan.f
+++ b/fvn_fnlib/ztan.f
@@ -1,7 +1,7 @@
       complex(8) function ztan (z)
       implicit none
 c march 1979 edition.  w. fullerton, c3, los alamos scientific lab.
-      complex z
+      complex(8) z
       real(8) d1mach,eps, xmax, ylarge, ybig, ymin,sn2x,den
       real(8) x,y,x2,y2
       integer irold,irold2