diff --git a/bootstrap.conf b/bootstrap.conf
index d8c7d128..b2d0f974 100644
--- a/bootstrap.conf
+++ b/bootstrap.conf
@@ -17,7 +17,8 @@
 
 # gnulib modules used by this package.
 gnulib_modules='
-  argmatch assert calloc-posix close closeout config-h c-strcase
+  argmatch assert assume
+  calloc-posix close closeout config-h c-strcase
   configmake
   dirname
   error extensions fdl fopen-safer
diff --git a/src/reader.c b/src/reader.c
index 18a3fc2d..12faef96 100644
--- a/src/reader.c
+++ b/src/reader.c
@@ -726,20 +726,20 @@ prepare_percent_define_front_end_variables (void)
 /* Find the first LHS which is not a dummy.  */
 
 static symbol *
-find_start_symbol ()
+find_start_symbol (void)
 {
   symbol_list *res = grammar;
   for (;
-       res != NULL && symbol_is_dummy (res->content.sym);
+       res && symbol_is_dummy (res->content.sym);
        res = res->next)
     {
       for (res = res->next;
-           res != NULL && res->content.sym != NULL;
+           res && res->content.sym;
            res = res->next)
         continue;
-      aver (res != NULL);
+      assume (res);
     }
-  aver (res != NULL);
+  assume (res);
   return res->content.sym;
 }