diff --git a/src/idl/dustem_write_isrf_lv.pro b/src/idl/dustem_write_isrf_lv.pro
index 4e5b399..ab109e2 100755
--- a/src/idl/dustem_write_isrf_lv.pro
+++ b/src/idl/dustem_write_isrf_lv.pro
@@ -119,7 +119,7 @@ IF ctpop NE 0 or ctusrisrf NE 0 THEN BEGIN
         c(2) = '# USER-DEFINED ISRF'
     ENDIF
     
-    IF G0_mathis EQ 0 THEN G0_mathis=1
+    IF G0_mathis EQ 0 THEN G0_mathis=1.
     
     ;the below condition will always be valid
     IF G0_mathis NE 0 THEN BEGIN 
--
libgit2 0.21.2