diff --git a/src/spicelib/devices/vdmos/vdmosdset.c b/src/spicelib/devices/vdmos/vdmosdset.c
index af2378ed5..23f587c79 100644
--- a/src/spicelib/devices/vdmos/vdmosdset.c
+++ b/src/spicelib/devices/vdmos/vdmosdset.c
@@ -99,7 +99,7 @@ VDMOSdSetup(GENmodel *inModel, CKTcircuit *ckt)
                 /* scale vds with mtr (except with lambda) */
                 double vdss = vds*mtr*here->VDMOSmode;
                 double t0 = 1 + lambda*vds;
-                double t1 = 1 + theta*vgs;
+                double t1 = 1 + theta*vgst;
                 double betap = Beta*t0/t1;
                 double dbetapdvgs = -Beta*theta*t0/(t1*t1);
                 double dbetapdvds = Beta*lambda/t1;