diff --git a/onnx/defs/schema.h b/onnx/defs/schema.h
index acf3aac..adae2d5 100644
--- a/onnx/defs/schema.h
+++ b/onnx/defs/schema.h
@@ -979,8 +979,10 @@ class OpSchemaRegistry final : public ISchemaRegistry {
 
   class OpSchemaRegisterOnce final {
    public:
-    // Export to cpp custom register macro
-    explicit OpSchemaRegisterOnce(
+    // Export to cpp custom register macro.
+    // DO NOT decorate the constructor as "explicit" because that breaks the macro ONNX_OPERATOR_SCHEMA_UNIQ.
+    // NOLINTNEXTLINE(google-explicit-constructor)
+    OpSchemaRegisterOnce( // NOSONAR
         OpSchema op_schema,
         int opset_version_to_load = 0,
         bool fail_duplicate_schema = true) {
@@ -1311,9 +1313,9 @@ size_t ReplaceAll(std::string& s, const char* from, const char* to);
 // Legacy macros to register schema at static initialization
 #define ONNX_OPERATOR_SCHEMA(name) ONNX_OPERATOR_SCHEMA_UNIQ_HELPER(__COUNTER__, name)
 #define ONNX_OPERATOR_SCHEMA_UNIQ_HELPER(Counter, name) ONNX_OPERATOR_SCHEMA_UNIQ(Counter, name)
-#define ONNX_OPERATOR_SCHEMA_UNIQ(Counter, name)                                                                      \
-  static ONNX_NAMESPACE::OpSchemaRegistry::OpSchemaRegisterOnce(op_schema_register_once##name##Counter) ONNX_UNUSED = \
-      OpSchema(#name, __FILE__, __LINE__)
+#define ONNX_OPERATOR_SCHEMA_UNIQ(Counter, name)                                                                     \
+  static ONNX_NAMESPACE::OpSchemaRegistry::OpSchemaRegisterOnce op_schema_register_once##name##Counter ONNX_UNUSED = \
+      ONNX_NAMESPACE::OpSchema(#name, __FILE__, __LINE__)
 
 // Helper function
 size_t ReplaceAll(std::string& s, const char* from, const char* to);