diff --git a/libpsx/include/stdio.h b/libpsx/include/stdio.h
index c63e585..456a438 100644
--- a/libpsx/include/stdio.h
+++ b/libpsx/include/stdio.h
@@ -112,7 +112,7 @@ FILE *fdopen(int fildes, const char *mode);
 FILE *fopen(const char *path, const char *mode);
 int fclose(FILE *stream);
 int fread(void *ptr, int size, int nmemb, FILE *f);
-int fwrite(void *ptr, int size, int nmemb, FILE *f);
+size_t fwrite(void *ptr, size_t size, size_t nmemb, FILE *stream);
 
 int fgetc(FILE *f);
 int ftell(FILE *f);
diff --git a/libpsx/src/libc.c b/libpsx/src/libc.c
index 55ab413..d8aef26 100644
--- a/libpsx/src/libc.c
+++ b/libpsx/src/libc.c
@@ -649,7 +649,8 @@ int puts(const char *str)
 	return EOF;
 }
 
-int fwrite(void *ptr, int size, int nmemb, FILE *f)
+size_t fwrite(void *restrict const ptr, const size_t size, const size_t nmemb,
+			  FILE *restrict const f)
 {
 	if(IS_CONS_OUT(f)) // stdout or stderr
 	{