Index: /issm/trunk-jpl/src/c/modules/SurfaceMassBalancex/Gembx.cpp
===================================================================
--- /issm/trunk-jpl/src/c/modules/SurfaceMassBalancex/Gembx.cpp	(revision 25998)
+++ /issm/trunk-jpl/src/c/modules/SurfaceMassBalancex/Gembx.cpp	(revision 25999)
@@ -1126,5 +1126,5 @@
 		// calculate surface shortwave radiation fluxes [W m-2]
 		if (aIdx == 1){
-			swf[0] = (1.0 - as) * dsw +  (1.0 - asdiff) * dswdiff;
+			swf[0] = (1.0 - as) * max(0.0,(dsw - dswdiff)) +  (1.0 - asdiff) * dswdiff;
 		}
 		else{