diff --git a/kernel/rtlil.h b/kernel/rtlil.h
index 827e3972b..992839f85 100644
--- a/kernel/rtlil.h
+++ b/kernel/rtlil.h
@@ -3079,6 +3079,8 @@ public:
 	const pool<PortBit> &fanout(SigBit bit);
 	const dict<SigBit, pool<PortBit>> &signorm_fanout() const;
 
+	bool signorm_indexed() const { return sig_norm_index != nullptr; }
+
 	const SigMap *signorm_sigmap();
 
 	// Equivalent to `connect(lhs, rhs)` followed by `sigNormalize()` for the
diff --git a/passes/cmds/check.cc b/passes/cmds/check.cc
index 128220f1c..d7d3f821f 100644
--- a/passes/cmds/check.cc
+++ b/passes/cmds/check.cc
@@ -31,7 +31,7 @@ PRIVATE_NAMESPACE_BEGIN
 int check_bufnorm_cell(RTLIL::Module *module, RTLIL::Cell *cell)
 {
 	bool bufnorm = module->design->flagBufferedNormalized;
-	bool signorm = module->design->flagSigNormalized;
+	bool signorm = module->design->flagSigNormalized && module->signorm_indexed();
 	if (!bufnorm && !signorm)
 		return 0;
 
@@ -102,7 +102,7 @@ int check_bufnorm_wire(RTLIL::Module *module, RTLIL::Wire *wire)
 
 int check_signorm_fanout(RTLIL::Module *module)
 {
-	if (!module->design->flagSigNormalized)
+	if (!module->design->flagSigNormalized || !module->signorm_indexed())
 		return 0;
 
 	int counter = 0;