diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index 737fb300c..46013544b 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -642,6 +642,7 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 	// (iterate by index as e.g. auto wires can add new children in the process)
 	for (size_t i = 0; i < children.size(); i++) {
 		bool did_something_here = true;
+		bool backup_flag_autowire = flag_autowire;
 		if ((type == AST_GENFOR || type == AST_FOR) && i >= 3)
 			break;
 		if ((type == AST_GENIF || type == AST_GENCASE) && i >= 1)
@@ -652,6 +653,8 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 			break;
 		if (type == AST_PREFIX && i >= 1)
 			break;
+		if (type == AST_DEFPARAM && i == 0)
+			flag_autowire = true;
 		while (did_something_here && i < children.size()) {
 			bool const_fold_here = const_fold, in_lvalue_here = in_lvalue;
 			int width_hint_here = width_hint;
@@ -686,6 +689,7 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 			children.erase(children.begin() + (i--));
 			did_something = true;
 		}
+		flag_autowire = backup_flag_autowire;
 	}
 	for (auto &attr : attributes) {
 		while (attr.second->simplify(true, false, false, stage, -1, false, true))
diff --git a/tests/simple/hierdefparam.v b/tests/simple/hierdefparam.v
index ff92c38bd..c9368ca7a 100644
--- a/tests/simple/hierdefparam.v
+++ b/tests/simple/hierdefparam.v
@@ -1,3 +1,5 @@
+`default_nettype none
+
 module hierdefparam_top(input [7:0] A, output [7:0] Y);
   generate begin:foo
     hierdefparam_a mod_a(.A(A), .Y(Y));