diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index 55087c772..749767743 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -1433,6 +1433,7 @@ bool AstNode::simplify(bool const_fold, int stage, int width_hint, bool sign_hin
 				current_ast_mod->children.push_back(wnode);
 			}
 			basic_prep = true;
+			is_custom_type = false;
 		}
 		break;
 
diff --git a/frontends/verilog/verilog_parser.y b/frontends/verilog/verilog_parser.y
index 9d0956c8e..68c3ec6ff 100644
--- a/frontends/verilog/verilog_parser.y
+++ b/frontends/verilog/verilog_parser.y
@@ -1855,7 +1855,7 @@ struct_decl:
 	}
 	;
 
-struct_type: struct_union { astbuf2 = $1; } struct_body { $$ = astbuf2; }
+struct_type: struct_union { astbuf2 = $1; astbuf2->is_custom_type = true; } struct_body { $$ = astbuf2; }
 	;
 
 struct_union: