diff --git a/file_io/include/aare/File.hpp b/file_io/include/aare/File.hpp
index 611c98c..a490598 100644
--- a/file_io/include/aare/File.hpp
+++ b/file_io/include/aare/File.hpp
@@ -12,7 +12,7 @@ template <DetectorType detector, typename DataType>
 class File {
 
   public:
-    virtual Frame<DataType>* get_frame(int frame_number) = 0;
+    virtual Frame<DataType>* get_frame(size_t frame_number) = 0;
 
   private:
   //comment
diff --git a/file_io/include/aare/JsonFile.hpp b/file_io/include/aare/JsonFile.hpp
index a878ebc..9dc0565 100644
--- a/file_io/include/aare/JsonFile.hpp
+++ b/file_io/include/aare/JsonFile.hpp
@@ -9,7 +9,7 @@ template <DetectorType detector, typename DataType> class JsonFile : public File
         using config = RawFileConfig;
                 public:
 
-    Frame<DataType> *get_frame(int frame_number);
+    Frame<DataType> *get_frame(size_t frame_number);
     int n_subfiles;
     std::vector<SubFile *> subfiles;
     int subfile_rows, subfile_cols;
diff --git a/file_io/include/aare/NumpyFile.hpp b/file_io/include/aare/NumpyFile.hpp
index a5a57b2..80c8d62 100644
--- a/file_io/include/aare/NumpyFile.hpp
+++ b/file_io/include/aare/NumpyFile.hpp
@@ -11,7 +11,7 @@ template <DetectorType detector, typename DataType> class NumpyFile : public Fil
     
   public:
     NumpyFile(std::filesystem::path fname);
-    Frame<DataType> *get_frame(int frame_number) override;
+    Frame<DataType> *get_frame(size_t frame_number) override;
     header_t header{};
     static constexpr std::array<char, 6> magic_str{'\x93', 'N', 'U', 'M', 'P', 'Y'};
     uint8_t major_ver_{};
diff --git a/file_io/src/JsonFile.cpp b/file_io/src/JsonFile.cpp
index 503b6fa..0b7844d 100644
--- a/file_io/src/JsonFile.cpp
+++ b/file_io/src/JsonFile.cpp
@@ -1,7 +1,7 @@
 #include "aare/JsonFile.hpp"
 
 template <DetectorType detector, typename DataType>
-Frame<DataType> *JsonFile<detector, DataType>::get_frame(int frame_number) {
+Frame<DataType> *JsonFile<detector, DataType>::get_frame(size_t frame_number) {
     if (frame_number > this->total_frames) {
         throw std::runtime_error("Frame number out of range");
     }
diff --git a/file_io/src/NumpyFile.cpp b/file_io/src/NumpyFile.cpp
index 245942e..15f06ff 100644
--- a/file_io/src/NumpyFile.cpp
+++ b/file_io/src/NumpyFile.cpp
@@ -2,13 +2,13 @@
 #include "aare/NumpyFile.hpp"
 
 template <DetectorType detector, typename DataType>
-NumpyFile<detector, DataType>::NumpyFile(std::filesystem::path fname){
-    this->fname = fname;
-    fp = fopen(fname.c_str(), "rb");
+NumpyFile<detector, DataType>::NumpyFile(std::filesystem::path fname_){
+    this->fname = fname_;
+    fp = fopen(this->fname.c_str(), "rb");
 }
 
 template <DetectorType detector, typename DataType>
-Frame<DataType> *NumpyFile<detector, DataType>::get_frame(int frame_number) {
+Frame<DataType> *NumpyFile<detector, DataType>::get_frame(size_t frame_number) {
     if (fp == nullptr) {
         throw std::runtime_error("File not open");
     }
diff --git a/file_io/src/NumpyFileFactory.cpp b/file_io/src/NumpyFileFactory.cpp
index 42e2056..1f912eb 100644
--- a/file_io/src/NumpyFileFactory.cpp
+++ b/file_io/src/NumpyFileFactory.cpp
@@ -78,12 +78,11 @@ template <DetectorType detector, typename DataType>
  File<detector, DataType>* NumpyFileFactory<detector, DataType>::load_file() {
     NumpyFile<detector, DataType> *file = new NumpyFile<detector, DataType>(this->m_fpath);
     parse_metadata(file);
-    NumpyFile<detector, DataType> *f = dynamic_cast<NumpyFile<detector, DataType> *>(file);
-    std::cout << "parsed header: " << f->header.to_string() << std::endl;
+    std::cout << "parsed header: " << file->header.to_string() << std::endl;
 
-    if(sizeof(DataType) != f->header.dtype.itemsize){
+    if(sizeof(DataType) != file->header.dtype.itemsize){
         std::stringstream  s;
-        s << "Data type size mismatch: " << sizeof(DataType) << " != " << f->header.dtype.itemsize;
+        s << "Data type size mismatch: " << sizeof(DataType) << " != " << file->header.dtype.itemsize;
         throw std::runtime_error(s.str());
     }       
     return file;