diff --git a/cpp/src/io/utilities/datasource.cpp b/cpp/src/io/utilities/datasource.cpp
index abc7a5ae056..8f2a5389b4d 100644
--- a/cpp/src/io/utilities/datasource.cpp
+++ b/cpp/src/io/utilities/datasource.cpp
@@ -25,6 +25,7 @@
 
 namespace cudf {
 namespace io {
+namespace {
 
 /**
  * @brief Base class for file input. Only implements direct device reads.
@@ -220,6 +221,8 @@ class user_datasource_wrapper : public datasource {
   datasource *const source;  ///< A non-owning pointer to the user-implemented datasource
 };
 
+}  // namespace
+
 std::unique_ptr<datasource> datasource::create(const std::string &filepath,
                                                size_t offset,
                                                size_t size)