diff --git a/elab_scope.cc b/elab_scope.cc
index d550340c4..e6d61de76 100644
--- a/elab_scope.cc
+++ b/elab_scope.cc
@@ -432,6 +432,9 @@ void PGModule::elaborate_scope_mod_(Design*des, Module*mod, NetScope*sc) const
 		       ; cur != replace.end() ;  cur ++ ) {
 
 		  PExpr*tmp = (*cur).second;
+		    // No expression means that the parameter is not
+		    // replaced at all.
+		  if (tmp == 0) continue;
 		  NetExpr*val = tmp->elaborate_pexpr(des, sc);
 		  bool flag = my_scope->replace_parameter((*cur).first, val);
 		  if (! flag) {
diff --git a/pform_dump.cc b/pform_dump.cc
index ed35bb791..ae17d6297 100644
--- a/pform_dump.cc
+++ b/pform_dump.cc
@@ -360,10 +360,14 @@ void PGModule::dump(ostream&out) const
       out << "    " << type_ << " ";
 
 	// If parameters are overridden by order, dump them.
-      if (overrides_) {
+      if (overrides_ && overrides_->count() > 0) {
 	    assert(parms_ == 0);
             out << "#(";
-	    out << *((*overrides_)[0]);
+
+	    if ((*overrides_)[0] == 0)
+	      out << "<nil>";
+	    else
+	      out << *((*overrides_)[0]);
 	    for (unsigned idx = 1 ;  idx < overrides_->count() ;  idx += 1) {
 	          out << "," << *((*overrides_)[idx]);
 	    }