diff --git a/f3read.c b/f3read.c
index 500cde9..1514365 100644
--- a/f3read.c
+++ b/f3read.c
@@ -1,4 +1,5 @@
 #define _POSIX_C_SOURCE 200112L
+#define _XOPEN_SOURCE 600
 
 #include <assert.h>
 #include <stdint.h>
@@ -10,6 +11,7 @@
 #include <fcntl.h>
 #include <unistd.h>
 #include <err.h>
+#include <sys/time.h>
 
 #include "utils.h"
 
diff --git a/f3write.c b/f3write.c
index 9d155a1..8cc9aaf 100644
--- a/f3write.c
+++ b/f3write.c
@@ -1,4 +1,5 @@
 #define _POSIX_C_SOURCE 200112L
+#define _XOPEN_SOURCE 600
 
 #include <assert.h>
 #include <stdint.h>
@@ -9,10 +10,10 @@
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <sys/statvfs.h>
+#include <sys/time.h>
 #include <errno.h>
 #include <unistd.h>
 #include <err.h>
-#include <alloca.h>
 #include <math.h>
 
 #include "utils.h"
@@ -341,7 +342,7 @@ static int create_and_fill_file(const char *path, long number, size_t size,
 	char *full_fn;
 	const char *filename;
 	int fd, fine;
-	void *buf;
+	char buf[fw->block_size];
 	size_t remaining;
 	uint64_t offset;
 	ssize_t written;
@@ -350,7 +351,7 @@ static int create_and_fill_file(const char *path, long number, size_t size,
 	assert(size % fw->block_size == 0);
 
 	/* Create the file. */
-	
+
 	fine = 0;
 	full_fn = full_fn_from_number(&filename, path, number);
 	assert(full_fn);
@@ -366,10 +367,6 @@ static int create_and_fill_file(const char *path, long number, size_t size,
 	}
 	assert(fd >= 0);
 
-	/* Obtain the buffer. */
-	buf = alloca(fw->block_size);
-	assert(buf);
-
 	/* Write content. */
 	fine = 1;
 	offset = (uint64_t)number * GIGABYTES;
@@ -392,7 +389,7 @@ static int create_and_fill_file(const char *path, long number, size_t size,
 	assert(!fine || remaining == 0);
 	end_measurement(fd, fw);
 	close(fd);
-	
+
 	printf("OK!\n");
 
 out:
diff --git a/utils.h b/utils.h
index 5803780..4593a86 100644
--- a/utils.h
+++ b/utils.h
@@ -67,4 +67,8 @@ static inline int posix_fadvise(int fd, off_t offset, off_t len, int advice)
 
 #endif	/* Apple Macintosh */
 
+#ifdef __FreeBSD__
+#define fdatasync(fd) fsync(fd)
+#endif
+
 #endif	/* HEADER_UTILS_H */