diff --git a/src/spicelib/devices/hisim2/hsm2eval.c b/src/spicelib/devices/hisim2/hsm2eval.c
index e10fd5f66..00caef669 100644
--- a/src/spicelib/devices/hisim2/hsm2eval.c
+++ b/src/spicelib/devices/hisim2/hsm2eval.c
@@ -205,6 +205,8 @@ double TMF1 , TMF2 , TMF3 , TMF4 ;
     TMF2 = sqrt ( ( x ) *  ( x ) + 4.0 * ( delta ) * ( delta) ) ; \
     dx = 0.5 * ( 1.0 + ( x ) / TMF2 ) ; \
     y = 0.5 * ( ( x ) + TMF2 ) ; \
+    if (y < 0) \
+        y = 0 ; \
   }
 #if 0
 /*---------------------------------------------------*
diff --git a/src/spicelib/devices/hisim2/hsm2temp.c b/src/spicelib/devices/hisim2/hsm2temp.c
index 4d851c22f..b71071fd9 100644
--- a/src/spicelib/devices/hisim2/hsm2temp.c
+++ b/src/spicelib/devices/hisim2/hsm2temp.c
@@ -41,6 +41,8 @@
 #define Fn_SZtemp( y , x , delta ) { \
     T1 = sqrt ( ( x ) *  ( x ) + 4.0 * ( delta ) * ( delta) ) ; \
     y = 0.5 * ( ( x ) + T1 ) ; \
+    if (y < 0) \
+        y = 0 ; \
   }
 
 #define Fn_SUtemp( y , x , xmax , delta ) { \