diff --git a/libs/ml/include/psemek/ml/neural_net/activation.hpp b/libs/ml/include/psemek/ml/neural_net/activation.hpp
index 186d645b..f336cdb9 100644
--- a/libs/ml/include/psemek/ml/neural_net/activation.hpp
+++ b/libs/ml/include/psemek/ml/neural_net/activation.hpp
@@ -19,7 +19,7 @@ namespace psemek::ml
 	struct unknown_activation_type
 		: std::exception
 	{
-		char const * what() noexcept;
+		char const * what() const noexcept override;
 	};
 
 	template <typename T>
diff --git a/libs/ml/source/neural_net/activation.cpp b/libs/ml/source/neural_net/activation.cpp
index d677776f..5fedabaf 100644
--- a/libs/ml/source/neural_net/activation.cpp
+++ b/libs/ml/source/neural_net/activation.cpp
@@ -3,7 +3,7 @@
 namespace psemek::ml
 {
 
-	char const * unknown_activation_type::what() noexcept
+	char const * unknown_activation_type::what() const noexcept
 	{
 		return "unknown activation type";
 	}