diff --git a/include/nbla/cuda/version.hpp b/include/nbla/cuda/version.hpp
index 736c98a8a..57d5e5f8e 100644
--- a/include/nbla/cuda/version.hpp
+++ b/include/nbla/cuda/version.hpp
@@ -15,6 +15,12 @@
 #ifndef _NBLA_EXT_CUDA_VERSION_HPP_
 #define _NBLA_EXT_CUDA_VERSION_HPP_
 
+#include <string>
+
+namespace nbla {
+
+using std::string;
+
 const string nbla_ext_cuda_version(void);
 
 const string nbla_ext_cuda_cuda_version(void);
@@ -24,4 +30,6 @@ const string nbla_ext_cuda_author(void);
 const string nbla_ext_cuda_author_email(void);
 const string nbla_ext_cuda_build_number(void);
 
+}
+
 #endif //_NBLA_EXT_CUDA_VERSION_HPP_