diff --git a/file/file.c b/file/file.c
index 179d933..22092ec 100644
--- a/file/file.c
+++ b/file/file.c
@@ -2,6 +2,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <fcntl.h>
+#include <unistd.h>
 
 #include "benchmark.h"
 
diff --git a/fork/fork.c b/fork/fork.c
index bca935c..900c2a8 100644
--- a/fork/fork.c
+++ b/fork/fork.c
@@ -1,5 +1,6 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include <unistd.h>
 
 // mesure copy-on-write, also with pthread
 
diff --git a/io/io.c b/io/io.c
index 9a9be73..a093b3c 100644
--- a/io/io.c
+++ b/io/io.c
@@ -11,8 +11,14 @@
 #define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <fcntl.h>
 
+#ifndef O_DIRECT
+#warning O_DIRECT not defined on this platform
+#define O_DIRECT 0
+#endif
+
 #include "benchmark.h"
 #include "copy.h"
 
diff --git a/lib/copy.c b/lib/copy.c
index 657ffbe..240302f 100644
--- a/lib/copy.c
+++ b/lib/copy.c
@@ -118,7 +118,9 @@ void read_write (timer *t, recorder *rec, char *in, char *out,
   char *s = NULL;
   err = posix_memalign((void **) &s, 512, len);
   if (err != 0) {
-    error(0, err, "posix_memalign");
+    // The value of errno is indeterminate after a call to posix_memalign()
+    errno = err; // so set it to use perror()
+    perror("posix_memalign");
     exit(EXIT_FAILURE);
   }
 
diff --git a/mmap/mmap.c b/mmap/mmap.c
index 7f3a5a9..c79b5c5 100644
--- a/mmap/mmap.c
+++ b/mmap/mmap.c
@@ -5,6 +5,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <unistd.h>
 
 #include "benchmark.h"
 #include "copy.h"
diff --git a/mutsem/mutsem.c b/mutsem/mutsem.c
index f85bac4..4def923 100644
--- a/mutsem/mutsem.c
+++ b/mutsem/mutsem.c
@@ -30,6 +30,7 @@
 #include <string.h>
 #include <semaphore.h>	
 #include <pthread.h>
+#include <unistd.h>
 
 #include "benchmark.h"
 
diff --git a/thread/thread.c b/thread/thread.c
index a8549eb..3cedef1 100644
--- a/thread/thread.c
+++ b/thread/thread.c
@@ -1,5 +1,6 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include <unistd.h>
 #include <pthread.h>
 
 #include "benchmark.h"