diff --git a/include/codata.h b/include/codata.h
index d65a77e..e578984 100644
--- a/include/codata.h
+++ b/include/codata.h
@@ -3,6 +3,8 @@
 * @brief Codata module - autogenerated.
 */
 
+#ifndef CODATA_H
+#define CODATA_H
 #if _MSC_VER
 #define ADD_IMPORT __declspec(dllimport)
 #else
@@ -1072,3 +1074,5 @@ ADD_IMPORT extern const double U_WIEN_WAVELENGTH_DISPLACEMENT_LAW_CONSTANT;/**<
 ADD_IMPORT extern const double W_TO_Z_MASS_RATIO;/**<  */
 ADD_IMPORT extern const double U_W_TO_Z_MASS_RATIO;/**<  */
 
+#endif
+
diff --git a/srcgen/c_code.f90 b/srcgen/c_code.f90
index 4babd98..376320e 100644
--- a/srcgen/c_code.f90
+++ b/srcgen/c_code.f90
@@ -14,6 +14,8 @@ subroutine write_c_header_doc(fcode)
     write(fcode, "(A) ") '* @brief Codata module - autogenerated.'
     write(fcode, "(A)") "*/"
     write(fcode, "(A)") ""
+    write(fcode, "(A)") '#ifndef CODATA_H'
+    write(fcode, "(A)") '#define CODATA_H'
     write(fcode, "(A)") "#if _MSC_VER"
     write(fcode, "(A)") "#define ADD_IMPORT __declspec(dllimport)"
     write(fcode, "(A)") "#else"
@@ -21,5 +23,15 @@ subroutine write_c_header_doc(fcode)
     write(fcode, "(A)") "#endif"
 end subroutine
 
+subroutine write_C_header_end(fcode)
+    !! Generate the C header declaration
+    implicit none
+    ! Arguments
+    integer(int32), intent(in) :: fcode
+        !! File unit of the C header.
+    write(fcode, "(A)") '#endif'
+    write(fcode, "(A)") ''
+end subroutine
+
 
 end module 
\ No newline at end of file
diff --git a/srcgen/main.f90 b/srcgen/main.f90
index 31d7e17..3d46877 100644
--- a/srcgen/main.f90
+++ b/srcgen/main.f90
@@ -80,6 +80,8 @@ program generator
 
     print *, "Writing fortran module end..."
     call write_fortran_module_end(ffortran)
+    print *, "Writing C header end..."
+    call write_C_header_end(fcheader)
     print *, "Writing cpython end..."
     call write_cpython_extension_end(fcpython);