diff --git a/include/eos/core/LandmarkMapper.hpp b/include/eos/core/LandmarkMapper.hpp
index bb4ab442..a99016d9 100644
--- a/include/eos/core/LandmarkMapper.hpp
+++ b/include/eos/core/LandmarkMapper.hpp
@@ -3,7 +3,7 @@
  *
  * File: include/eos/core/LandmarkMapper.hpp
  *
- * Copyright 2014-2017 Patrik Huber
+ * Copyright 2014-2024 Patrik Huber
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,6 +29,7 @@
 #include <stdexcept>
 #include <string>
 #include <unordered_map>
+#include <algorithm>
 
 namespace eos {
 namespace core {
@@ -156,6 +157,57 @@ class LandmarkMapper
                                                                     ///< in a different format.
 };
 
+
+/**
+ * @brief Gets the vertex index from the given landmark name using the landmark mapper and if provided the
+ * landmark definitions.
+ *
+ * The function only returns the vertex index if the landmark mapper was able to convert the name.
+ *
+ * @param[in] landmark_name Name of the landmark, often used as identifier.
+ * @param[in] landmark_mapper A mapper which maps the 2D landmark identifiers to 3D model vertex indices.
+ * @param[in] landmark_definitions A set of landmark definitions for the model, mapping from identifiers to
+ * vertex indices.
+ * @return An optional int with the vertex index.
+ */
+inline cpp17::optional<int>
+get_vertex_index(const std::string landmark_name, const core::LandmarkMapper& landmark_mapper,
+                 const cpp17::optional<std::unordered_map<std::string, int>>& landmark_definitions)
+{
+    const auto converted_name = landmark_mapper.convert(landmark_name);
+    if (!converted_name)
+    { // no mapping defined for the current landmark
+        return std::nullopt;
+    }
+    // If the MorphableModel does not contain landmark definitions, we expect the user to have given us
+    // direct mappings (e.g. directly from ibug identifiers to vertex ids). If the model does contain
+    // landmark definitions, we expect the user to use mappings from their landmark identifiers (e.g.
+    // ibug) to the landmark definitions. Users may also include direct mappings to create a "hybrid" mapping.
+    // Todo: This might be worth mentioning in the function documentation of fit_shape_and_pose.
+    int vertex_idx;
+    if (std::all_of(converted_name.value().begin(), converted_name.value().end(), ::isdigit))
+    {
+        vertex_idx = std::stoi(converted_name.value());
+    } else
+    {
+        if (landmark_definitions)
+        {
+            const auto found_vertex_idx = landmark_definitions.value().find(converted_name.value());
+            if (found_vertex_idx != std::end(landmark_definitions.value()))
+            {
+                vertex_idx = found_vertex_idx->second;
+            } else
+            {
+                return cpp17::nullopt;
+            }
+        } else
+        {
+            return cpp17::nullopt;
+        }
+    }
+    return vertex_idx;
+};
+
 } /* namespace core */
 } /* namespace eos */
 
diff --git a/include/eos/fitting/fitting.hpp b/include/eos/fitting/fitting.hpp
index f8a7c49c..b5dc5f20 100644
--- a/include/eos/fitting/fitting.hpp
+++ b/include/eos/fitting/fitting.hpp
@@ -149,53 +149,6 @@ inline Eigen::VectorXf fit_shape(Eigen::Matrix<float, 3, 4> affine_camera_matrix
                      num_coefficients_to_fit, unused, unused);
 };
 
-/**
- * @brief Gets the vertex index from the given landmark name using the landmark mapper and if provided the landmark definitions.
- *
- * The function only returns the vertex index if the landmark mapper was able to convert the name.
- *
- * @param[in] landmark_name Name of the landmark, often used as identifier.
- * @param[in] landmark_mapper A mapper which maps the 2D landmark identifiers to 3D model vertex indices.
- * @param[in] landmark_definitions A set of landmark definitions for the model, mapping from identifiers to vertex indices.
- * @return An optional int with the vertex index.
- */
-inline cpp17::optional<int> get_vertex_index(const std::string landmark_name, const core::LandmarkMapper& landmark_mapper, 
-                            const cpp17::optional<std::unordered_map<std::string, int>>& landmark_definitions)
-{
-    const auto converted_name = landmark_mapper.convert(landmark_name);
-    if (!converted_name)
-    { // no mapping defined for the current landmark
-        return std::nullopt;
-    }
-    // If the MorphableModel does not contain landmark definitions, we expect the user to have given us
-    // direct mappings (e.g. directly from ibug identifiers to vertex ids). If the model does contain
-    // landmark definitions, we expect the user to use mappings from their landmark identifiers (e.g.
-    // ibug) to the landmark definitions. Users may also include direct mappings to create a "hybrid" mapping.
-    // Todo: This might be worth mentioning in the function documentation of fit_shape_and_pose.
-    int vertex_idx;
-    if (std::all_of(converted_name.value().begin(), converted_name.value().end(), ::isdigit))
-    {
-        vertex_idx = std::stoi(converted_name.value());
-    } else
-    {
-        if (landmark_definitions)
-        {
-            const auto found_vertex_idx = landmark_definitions.value().find(converted_name.value());
-            if (found_vertex_idx != std::end(landmark_definitions.value()))
-            {
-                vertex_idx = found_vertex_idx->second;
-            } else
-            {
-                return cpp17::nullopt;
-            }
-        } else
-        {
-            return cpp17::nullopt;
-        }
-    }
-    return vertex_idx;
-}
-
 /**
  * @brief Fits the given expression model to landmarks.
  *
@@ -366,7 +319,8 @@ inline std::pair<core::Mesh, fitting::RenderingParameters> fit_shape_and_pose(
     // and get the corresponding model points (mean if given no initial coeffs, from the computed shape otherwise):
     for (int i = 0; i < landmarks.size(); ++i)
     {
-        const cpp17::optional<int> vertex_idx = get_vertex_index(landmarks[i].name, landmark_mapper, morphable_model.get_landmark_definitions());
+        const cpp17::optional<int> vertex_idx = core::get_vertex_index(
+            landmarks[i].name, landmark_mapper, morphable_model.get_landmark_definitions());
         if (!vertex_idx) // vertex index not defined for the current landmark
         {
             continue;
@@ -830,7 +784,8 @@ inline std::pair<core::Mesh, fitting::RenderingParameters> fit_shape_and_pose(
     // and get the corresponding model points (mean if given no initial coeffs, from the computed shape otherwise):
     for (int i = 0; i < landmarks.size(); ++i)
     {
-        const cpp17::optional<int> vertex_idx = get_vertex_index(landmarks[i].name, landmark_mapper, morphable_model.get_landmark_definitions());
+        const cpp17::optional<int> vertex_idx = core::get_vertex_index(
+            landmarks[i].name, landmark_mapper, morphable_model.get_landmark_definitions());
         if (!vertex_idx) // vertex index not defined for the current landmark
         {
             continue;