diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index 982d1ae3..9b8ed760 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -497,8 +497,9 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
 		if (width != int(children[0]->bits.size())) {
 			RTLIL::SigSpec sig(children[0]->bits);
 			sig.extend_u0(width, children[0]->is_signed);
-			delete children[0];
+			AstNode *old_child_0 = children[0];
 			children[0] = mkconst_bits(sig.as_const().bits, children[0]->is_signed);
+			delete old_child_0;
 		}
 		children[0]->is_signed = is_signed;
 	}