diff --git a/parse.c b/parse.c
index 6e9907c2a7562eb28ebe972a2773da00076ec0c6..dcfd08838b3856c661089fc016b24c7c3376d1e5 100644
--- a/parse.c
+++ b/parse.c
@@ -206,7 +206,8 @@ trim_and_sub (Package *pkg, const char *str, const char *path)
 
           g_free (varname);
 
-          g_string_append (subst, varval);
+          if (varval)
+            g_string_append (subst, varval);
           g_free (varval);
         }
       else