diff --git a/passes/hierarchy/hierarchy.cc b/passes/hierarchy/hierarchy.cc
index dceda1624..08b14dca0 100644
--- a/passes/hierarchy/hierarchy.cc
+++ b/passes/hierarchy/hierarchy.cc
@@ -684,30 +684,24 @@ void hierarchy_clean(RTLIL::Design *design, RTLIL::Module *top, bool purge_lib)
 
 bool set_keep_print(std::map<RTLIL::Module*, bool> &cache, RTLIL::Module *mod)
 {
-	auto it = cache.find(mod);
-	if (it != cache.end())
-		return it->second;
-	cache[mod] = false;
-	for (auto c : mod->cells()) {
-		RTLIL::Module *m = mod->design->module(c->type);
-		if ((m != nullptr && set_keep_print(cache, m)) || c->type == ID($print))
-			return cache[mod] = true;
-	}
-	return false;
+	if (cache.count(mod) == 0)
+		for (auto c : mod->cells()) {
+			RTLIL::Module *m = mod->design->module(c->type);
+			if ((m != nullptr && set_keep_print(cache, m)) || c->type == ID($print))
+				return cache[mod] = true;
+		}
+	return cache[mod];
 }
 
 bool set_keep_assert(std::map<RTLIL::Module*, bool> &cache, RTLIL::Module *mod)
 {
-	auto it = cache.find(mod);
-	if (it != cache.end())
-		return it->second;
-	cache[mod] = false;
-	for (auto c : mod->cells()) {
-		RTLIL::Module *m = mod->design->module(c->type);
-		if ((m != nullptr && set_keep_assert(cache, m)) || c->type.in(ID($check), ID($assert), ID($assume), ID($live), ID($fair), ID($cover)))
-			return cache[mod] = true;
-	}
-	return false;
+	if (cache.count(mod) == 0)
+		for (auto c : mod->cells()) {
+			RTLIL::Module *m = mod->design->module(c->type);
+			if ((m != nullptr && set_keep_assert(cache, m)) || c->type.in(ID($check), ID($assert), ID($assume), ID($live), ID($fair), ID($cover)))
+				return cache[mod] = true;
+		}
+	return cache[mod];
 }
 
 int find_top_mod_score(Design *design, Module *module, dict<Module*, int> &db)