diff --git a/extensions/iidm/src/BranchObservability.cpp b/extensions/iidm/src/BranchObservability.cpp
index 37a26026..1855cf1f 100644
--- a/extensions/iidm/src/BranchObservability.cpp
+++ b/extensions/iidm/src/BranchObservability.cpp
@@ -34,35 +34,35 @@ const std::string& BranchObservability::getName() const {
 }
 
 stdcxx::CReference<ObservabilityQuality> BranchObservability::getQualityP1() const {
-    return stdcxx::cref(m_qualityP1);
+    return stdcxx::cref<ObservabilityQuality>(m_qualityP1);
 }
 
 stdcxx::Reference<ObservabilityQuality> BranchObservability::getQualityP1() {
-    return stdcxx::ref(m_qualityP1);
+    return stdcxx::ref<ObservabilityQuality>(m_qualityP1);
 }
 
 stdcxx::CReference<ObservabilityQuality> BranchObservability::getQualityP2() const {
-    return stdcxx::cref(m_qualityP2);
+    return stdcxx::cref<ObservabilityQuality>(m_qualityP2);
 }
 
 stdcxx::Reference<ObservabilityQuality> BranchObservability::getQualityP2() {
-    return stdcxx::ref(m_qualityP2);
+    return stdcxx::ref<ObservabilityQuality>(m_qualityP2);
 }
 
 stdcxx::CReference<ObservabilityQuality> BranchObservability::getQualityQ1() const {
-    return stdcxx::cref(m_qualityQ1);
+    return stdcxx::cref<ObservabilityQuality>(m_qualityQ1);
 }
 
 stdcxx::Reference<ObservabilityQuality> BranchObservability::getQualityQ1() {
-    return stdcxx::ref(m_qualityQ1);
+    return stdcxx::ref<ObservabilityQuality>(m_qualityQ1);
 }
 
 stdcxx::CReference<ObservabilityQuality> BranchObservability::getQualityQ2() const {
-    return stdcxx::cref(m_qualityQ2);
+    return stdcxx::cref<ObservabilityQuality>(m_qualityQ2);
 }
 
 stdcxx::Reference<ObservabilityQuality> BranchObservability::getQualityQ2() {
-    return stdcxx::ref(m_qualityQ2);
+    return stdcxx::ref<ObservabilityQuality>(m_qualityQ2);
 }
 
 const std::type_index& BranchObservability::getType() const {
diff --git a/include/powsybl/stdcxx/reference.hpp b/include/powsybl/stdcxx/reference.hpp
index ce81b0cf..dde1c370 100644
--- a/include/powsybl/stdcxx/reference.hpp
+++ b/include/powsybl/stdcxx/reference.hpp
@@ -108,8 +108,8 @@ CReference<T> cref(const std::unique_ptr<T>& pointer) {
     return static_cast<bool>(pointer) ? CReference<T>(*pointer) : CReference<T>();
 }
 
-template <typename T, typename = typename std::enable_if<!std::is_abstract<T>::value>::type>
-CReference<T> cref(const stdcxx::optional<T>& optional) {
+template <typename T, typename U, typename = typename std::enable_if<!std::is_abstract<U>::value && std::is_same<T, U>::value>::type>
+CReference<T> cref(const stdcxx::optional<U>& optional) {
     return static_cast<bool>(optional) ? CReference<T>(*optional) : CReference<T>();
 }
 
@@ -138,8 +138,8 @@ Reference<T> ref(const std::unique_ptr<T>& pointer) {
     return static_cast<bool>(pointer) ? Reference<T>(*pointer) : Reference<T>();
 }
 
-template <typename T, typename = typename std::enable_if<!std::is_abstract<T>::value>::type>
-Reference<T> ref(stdcxx::optional<T>& optional) {
+template <typename T, typename U, typename = typename std::enable_if<!std::is_abstract<U>::value && std::is_same<T, U>::value>::type>
+Reference<T> ref(stdcxx::optional<U>& optional) {
     return static_cast<bool>(optional) ? Reference<T>(*optional) : Reference<T>();
 }