diff --git a/libpsx/include/stdio.h b/libpsx/include/stdio.h
index 34d2d57..b0979cc 100644
--- a/libpsx/include/stdio.h
+++ b/libpsx/include/stdio.h
@@ -118,7 +118,7 @@ FILE *fdopen(int fildes, const char *mode);
 FILE *fopen(const char *path, const char *mode);
 int fclose(FILE *stream);
 size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);
-size_t fwrite(void *ptr, size_t size, size_t nmemb, FILE *stream);
+size_t fwrite(const 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 58884b0..5c4b17a 100644
--- a/libpsx/src/libc.c
+++ b/libpsx/src/libc.c
@@ -722,12 +722,12 @@ int puts(const char *str)
 	return EOF;
 }
 
-size_t fwrite(void *restrict const ptr, const size_t size, const size_t nmemb,
+size_t fwrite(const void *restrict const ptr, const size_t size, const size_t nmemb,
 			  FILE *restrict const f)
 {
 	if(IS_CONS_OUT(f)) // stdout or stderr
 	{
-		char *c = ptr;
+		const char *c = ptr;
 		int i;
 
 		for(i = 0; i < size; i++)