diff --git a/src/sequence_diagram/model/diagram.h b/src/sequence_diagram/model/diagram.h
index a26a31c4..ea3c6b58 100644
--- a/src/sequence_diagram/model/diagram.h
+++ b/src/sequence_diagram/model/diagram.h
@@ -63,7 +63,7 @@ public:
     }
 
     template <typename T>
-    const common::optional_ref<T> get_participant(
+    common::optional_ref<T> get_participant(
         common::model::diagram_element::id_t id) const
     {
         if (participants_.find(id) == participants_.end()) {
diff --git a/src/sequence_diagram/model/participant.cc b/src/sequence_diagram/model/participant.cc
index e941330d..11f548b8 100644
--- a/src/sequence_diagram/model/participant.cc
+++ b/src/sequence_diagram/model/participant.cc
@@ -234,7 +234,7 @@ method::method(const common::model::namespace_ &using_namespace)
 {
 }
 
-const std::string method::method_name() const { return method_name_; }
+std::string method::method_name() const { return method_name_; }
 
 std::string method::alias() const
 {
diff --git a/src/sequence_diagram/model/participant.h b/src/sequence_diagram/model/participant.h
index e5b518a7..bad86e8b 100644
--- a/src/sequence_diagram/model/participant.h
+++ b/src/sequence_diagram/model/participant.h
@@ -185,7 +185,7 @@ struct method : public function {
 
     std::string type_name() const override { return "method"; }
 
-    const std::string method_name() const;
+    std::string method_name() const;
 
     std::string alias() const override;
 
diff --git a/src/sequence_diagram/visitor/translation_unit_visitor.h b/src/sequence_diagram/visitor/translation_unit_visitor.h
index 8b87fe16..ab396b76 100644
--- a/src/sequence_diagram/visitor/translation_unit_visitor.h
+++ b/src/sequence_diagram/visitor/translation_unit_visitor.h
@@ -120,7 +120,7 @@ public:
     }
 
     template <typename T = model::participant>
-    const common::optional_ref<T> get_participant(const clang::Decl *decl) const
+    common::optional_ref<T> get_participant(const clang::Decl *decl) const
     {
         assert(decl != nullptr);
 
@@ -143,7 +143,7 @@ public:
     }
 
     template <typename T = model::participant>
-    const common::optional_ref<T> get_participant(
+    common::optional_ref<T> get_participant(
         common::model::diagram_element::id_t id) const
     {
         if (diagram().participants().find(id) == diagram().participants().end())