diff --git a/elab_pexpr.cc b/elab_pexpr.cc
index 553e776c2..1231119a7 100644
--- a/elab_pexpr.cc
+++ b/elab_pexpr.cc
@@ -508,7 +508,7 @@ void NetEParam::resolve_pexpr_type(void)
       if (reference_->second.signed_flag) {
 	    cast_signed_base_(true);
 
-      } else {
+      } else if (reference_->second.expr) {
 	    cast_signed_base_( reference_->second.expr->has_sign() );
       }
 }
diff --git a/eval_tree.cc b/eval_tree.cc
index 38c37dca3..6f744f452 100644
--- a/eval_tree.cc
+++ b/eval_tree.cc
@@ -1231,7 +1231,15 @@ NetExpr* NetEParam::eval_tree(int prune_to_width)
       assert(scope_);
       perm_string name = (*reference_).first;
       const NetExpr*expr = (*reference_).second.expr;
-      ivl_assert(*this, expr);
+	// Since constant user functions are not supported we can get
+	// parameters/localparams that are not defined. For now generate
+	// an appropriate error message.
+      if (expr == NULL) {
+	    cerr << get_fileline() << ": internal error: parameter/localparam "
+		 << *this << " cannot be evaluated." << endl;
+	    return 0;
+      }
+//      ivl_assert(*this, expr);
 
       NetExpr*nexpr = expr->dup_expr();
       assert(nexpr);