diff --git a/utils.c b/utils.c
index d4e733f..03691c0 100644
--- a/utils.c
+++ b/utils.c
@@ -1,8 +1,19 @@
 #define _GNU_SOURCE
 
+#if __APPLE__ && __MACH__
+
+#define _DARWIN_C_SOURCE
+
+#include <fcntl.h>	/* For function fcntl.	*/
+
+#endif	/* Apple Macintosh */
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <ctype.h>
+#include <assert.h>
+#include <limits.h>
 #include <sys/types.h>
 #include <dirent.h>
 #include <errno.h>
@@ -215,3 +226,26 @@ void print_header(FILE *f, const char *name)
 	"This is free software; see the source for copying conditions.\n"
 	"\n", name);
 }
+
+#if __APPLE__ && __MACH__
+
+/* This function is a _rough_ approximation of fdatasync(2). */
+static inline int fdatasync(int fd)
+{
+	return fcntl(fd, F_FULLFSYNC);
+}
+
+/* This function is a _rough_ approximation of posix_fadvise(2). */
+int posix_fadvise(int fd, off_t offset, off_t len, int advice)
+{
+	switch (advice) {
+	case POSIX_FADV_SEQUENTIAL:
+		return fcntl(fd, F_RDAHEAD, 1);
+	case POSIX_FADV_DONTNEED:
+		return fcntl(fd, F_NOCACHE, 1);
+	default:
+		assert(0);
+	}
+}
+
+#endif	/* Apple Macintosh */
diff --git a/utils.h b/utils.h
index 693e48a..8ce8e9a 100644
--- a/utils.h
+++ b/utils.h
@@ -1,11 +1,9 @@
 #ifndef HEADER_UTILS_H
 #define HEADER_UTILS_H
 
-#include <ctype.h>
-#include <assert.h>
-#include <sys/time.h>
-#include <limits.h>
-#include <stdint.h>
+#include <stdio.h>	/* For type FILE.	*/
+#include <sys/time.h>	/* For struct timeval.	*/
+#include <stdint.h>	/* For type uint64_t.	*/
 
 #define SECTOR_SIZE (512)
 #define GIGABYTES   (1024 * 1024 * 1024)
@@ -38,34 +36,13 @@ static inline uint64_t random_number(uint64_t prv_number)
 
 #if __APPLE__ && __MACH__
 
-#define _DARWIN_C_SOURCE
-
-/* For function fcntl. */
-#include <fcntl.h>
-/* For type off_t. */
-#include <unistd.h>
-
-/* This function is a _rough_ approximation of fdatasync(2). */
-static inline int fdatasync(int fd)
-{
-	return fcntl(fd, F_FULLFSYNC);
-}
+#include <unistd.h>	/* For type off_t.	*/
 
 #define POSIX_FADV_SEQUENTIAL	2 /* Expect sequential page references.	*/
 #define POSIX_FADV_DONTNEED	4 /* Don't need these pages.		*/
 
-/* This function is a _rough_ approximation of posix_fadvise(2). */
-static inline int posix_fadvise(int fd, off_t offset, off_t len, int advice)
-{
-	switch (advice) {
-	case POSIX_FADV_SEQUENTIAL:
-		return fcntl(fd, F_RDAHEAD, 1);
-	case POSIX_FADV_DONTNEED:
-		return fcntl(fd, F_NOCACHE, 1);
-	default:
-		assert(0);
-	}
-}
+int fdatasync(int fd);
+int posix_fadvise(int fd, off_t offset, off_t len, int advice);
 
 #endif	/* Apple Macintosh */