diff --git a/docs/porting-guide.md b/docs/porting-guide.md
index c369844..db6038a 100644
--- a/docs/porting-guide.md
+++ b/docs/porting-guide.md
@@ -358,13 +358,12 @@
 
     Defines the maximum number of registered IO devices. Attempting to register
     more devices than this value using `io_register_device()` will fail with
-    IO_RESOURCES_EXHAUSTED.
+    -ENOMEM.
 
 *   **#define : MAX_IO_HANDLES**
 
     Defines the maximum number of open IO handles. Attempting to open more IO
-    entities than this value using `io_open()` will fail with
-    IO_RESOURCES_EXHAUSTED.
+    entities than this value using `io_open()` will fail with -ENOMEM.
 
 If the platform needs to allocate data within the per-cpu data framework in
 BL3-1, it should define the following macro. Currently this is only required if
diff --git a/include/drivers/io/io_storage.h b/include/drivers/io/io_storage.h
index e98dcd0..4c3526e 100644
--- a/include/drivers/io/io_storage.h
+++ b/include/drivers/io/io_storage.h
@@ -31,6 +31,7 @@
 #ifndef __IO_H__
 #define __IO_H__
 
+#include <errno.h>
 #include <stdint.h>
 #include <stdio.h> /* For ssize_t */
 #include <uuid.h>
@@ -88,11 +89,13 @@
 #define IO_MODE_RW	(1 << 1)
 
 
-/* Return codes reported by 'io_*' APIs */
+/* Return codes reported by 'io_*' APIs.
+ * IMPORTANT: these definitions are deprecated. Callers should use standard
+ * errno definitions when checking the return value of io_* APIs. */
 #define IO_SUCCESS		(0)
-#define IO_FAIL			(-1)
-#define IO_NOT_SUPPORTED	(-2)
-#define IO_RESOURCES_EXHAUSTED	(-3)
+#define IO_FAIL			(-ENOENT)
+#define IO_NOT_SUPPORTED	(-ENODEV)
+#define IO_RESOURCES_EXHAUSTED	(-ENOMEM)
 
 
 /* Open a connection to a device */