diff --git a/src/H5Format.hpp b/src/H5Format.hpp
index dad8d46..2161a4d 100644
--- a/src/H5Format.hpp
+++ b/src/H5Format.hpp
@@ -93,7 +93,7 @@ class H5Format
 
         virtual const std::unordered_map<std::string, boost::any>& get_default_values() const = 0;
 
-        virtual const h5_group& get_format_definition() const = 0;
+        virtual const h5_parent& get_format_definition() const = 0;
 
         virtual void add_calculated_values(std::unordered_map<std::string, boost::any>& values) const = 0;
 
diff --git a/src/format/NXmxFormat.cpp b/src/format/NXmxFormat.cpp
index 3879038..8c6e45a 100644
--- a/src/format/NXmxFormat.cpp
+++ b/src/format/NXmxFormat.cpp
@@ -15,7 +15,7 @@ class NXmxFormat : public H5Format
     shared_ptr<unordered_map<string, DATA_TYPE>> input_value_type = NULL;
     shared_ptr<unordered_map<string, boost::any>> default_values = NULL;
     shared_ptr<unordered_map<string, std::string>> dataset_move_mapping = NULL;
-    shared_ptr<h5_group> file_format = NULL;
+    shared_ptr<h5_parent> file_format = NULL;
 
     public:
         ~NXmxFormat(){};
@@ -904,7 +904,7 @@ class NXmxFormat : public H5Format
             }));
         }
 
-        const h5_group& get_format_definition() const override {
+        const h5_parent& get_format_definition() const override {
             return *file_format;
         }