[C] syntax error before "MYSTRUCT"

[gaten]

file1.h

#ifndef FILE1_H
#define FILE1_H

typedef struct _mystruct {
...
} MYSTRUCT;

...


#endif

file2.h

#ifndef FILE2_H
#define FILE2_H

#include "file1.h"

...
void foo( MYSTRUCT s );

#endif

mi dà il seguente errore:

17 C:\Users\Gaten\Desktop\Fuga\file2.h syntax error before "MYSTRUCT"

come mai