diff --git a/passes/opt/opt_clean.cc b/passes/opt/opt_clean.cc
index bf8020169..7011d4602 100644
--- a/passes/opt/opt_clean.cc
+++ b/passes/opt/opt_clean.cc
@@ -319,8 +319,9 @@ bool rmunused_module_signals(RTLIL::Module *module, bool purge_mode, bool verbos
 			wire->attributes.erase("\\init");
 
 		if (GetSize(wire) == 0) {
-			// delete zero-width wires
-			goto delete_this_wire;
+			// delete zero-width wires, unless they are module ports
+			if (wire->port_id == 0)
+				goto delete_this_wire;
 		} else
 		if (wire->port_id != 0 || wire->get_bool_attribute("\\keep") || !initval.is_fully_undef()) {
 			// do not delete anything with "keep" or module ports or initialized wires