diff --git a/src/include/file_io.h b/src/include/file_io.h
index 2ae3a28abd14f409f5f28aa0857d65247ac67c10..24f2c5f0cff1165afacbea0b5d2ac443fd0f6df7 100644
--- a/src/include/file_io.h
+++ b/src/include/file_io.h
@@ -10,34 +10,34 @@
  * \param sta: `char*` C-string for file status (max. length of 7).
  * \param mode: `char*` C-string for access mode (max. length of 11).
  */
-extern "C" void open_file_(int*, const char*, const char*, const char*);
+extern "C" void open_file_(int* uid, const char* name, const char* sta, const char* mode);
 /*! \brief Close a previously opened file.
  *
  * \param uid: `int*` Pointer to the unit ID of the file.
  */
-extern "C" void close_file_(int*);
+extern "C" void close_file_(int* uid);
 /*! \brief Read an integer value from a file.
  *
  * \param uid: `int*` Pointer to the unit ID of the file.
  * \param value: `int*` Pointer of the variable to be updated.
  */
-extern "C" void read_int_(int*, int*);
+extern "C" void read_int_(int* uid, int* value);
 /*! \brief Write a complex value to a file.
  *
  * \param uid: `int*` Pointer to the unit ID of the file.
  * \param real: `double*` Pointer to the real part of the value.
  * \param imag: `double*` Pointer to the imaginary part of the value.
  */
-extern "C" void write_complex_(int*, double*, double*);
+extern "C" void write_complex_(int* uid, double* real, double* imag);
 /*! \brief Write a double precision float value to a file.
  *
  * \param uid: `int*` Pointer to the unit ID of the file.
  * \param value: `double*` Pointer to the variable to be written.
  */
-extern "C" void write_double_(int*, double*);
+extern "C" void write_double_(int* uid, double* value);
 /*! \brief Write an integer value to a file.
  *
  * \param uid: `int*` Pointer to the unit ID of the file.
  * \param value: `int*` Pointer to the variable to be written.
  */
-extern "C" void write_int_(int*, int*);
+extern "C" void write_int_(int* uid, int* value);