diff --git a/include/eigenpy/deprecation-policy.hpp b/include/eigenpy/deprecation-policy.hpp
index 42de0213cc56cc93d1add046591c4836577ecb2c..e1e953f5a328ce492fa98cec6a187b281c81fb3f 100644
--- a/include/eigenpy/deprecation-policy.hpp
+++ b/include/eigenpy/deprecation-policy.hpp
@@ -13,7 +13,7 @@ enum class DeprecationType { DEPRECATION, FUTURE };
 
 namespace detail {
 
-PyObject *deprecationTypeToPyObj(DeprecationType dep) {
+inline PyObject *deprecationTypeToPyObj(DeprecationType dep) {
   switch (dep) {
     case DeprecationType::DEPRECATION:
       return PyExc_DeprecationWarning;