diff --git a/include/drivers/io_driver.h b/include/drivers/io_driver.h
index cc01d3b..f34c71d 100644
--- a/include/drivers/io_driver.h
+++ b/include/drivers/io_driver.h
@@ -39,7 +39,7 @@
 /* Generic IO entity structure,representing an accessible IO construct on the
  * device, such as a file */
 typedef struct io_entity {
-	io_dev_handle dev_handle;
+	struct io_dev_info *dev_handle;
 	uintptr_t info;
 } io_entity_t;
 
@@ -47,7 +47,7 @@
 /* Device info structure, providing device-specific functions and a means of
  * adding driver-specific state */
 typedef struct io_dev_info {
-	struct io_dev_funcs *funcs;
+	const struct io_dev_funcs *funcs;
 	uintptr_t info;
 } io_dev_info_t;
 
@@ -55,23 +55,23 @@
 /* Structure used to create a connection to a type of device */
 typedef struct io_dev_connector {
 	/* dev_open opens a connection to a particular device driver */
-	int (*dev_open)(void *spec, io_dev_info_t **dev_info);
+	int (*dev_open)(const uintptr_t dev_spec, io_dev_info_t **dev_info);
 } io_dev_connector_t;
 
 
 /* Structure to hold device driver function pointers */
 typedef struct io_dev_funcs {
 	io_type_t (*type)(void);
-	int (*open)(io_dev_info_t *dev_info, const void *spec,
+	int (*open)(io_dev_info_t *dev_info, const uintptr_t spec,
 			io_entity_t *entity);
 	int (*seek)(io_entity_t *entity, int mode, ssize_t offset);
 	int (*size)(io_entity_t *entity, size_t *length);
-	int (*read)(io_entity_t *entity, void *buffer, size_t length,
+	int (*read)(io_entity_t *entity, uintptr_t buffer, size_t length,
 			size_t *length_read);
-	int (*write)(io_entity_t *entity, const void *buffer,
+	int (*write)(io_entity_t *entity, const uintptr_t buffer,
 			size_t length, size_t *length_written);
 	int (*close)(io_entity_t *entity);
-	int (*dev_init)(io_dev_info_t *dev_info, const void *init_params);
+	int (*dev_init)(io_dev_info_t *dev_info, const uintptr_t init_params);
 	int (*dev_close)(io_dev_info_t *dev_info);
 } io_dev_funcs_t;
 
@@ -79,7 +79,7 @@
 /* IO platform data - used to track devices registered for a specific
  * platform */
 typedef struct io_plat_data {
-	io_dev_info_t *devices[MAX_IO_DEVICES];
+	const io_dev_info_t *devices[MAX_IO_DEVICES];
 	unsigned int dev_count;
 } io_plat_data_t;
 
@@ -90,6 +90,6 @@
 void io_init(io_plat_data_t *data);
 
 /* Register a device driver */
-int io_register_device(io_dev_info_t *dev_info);
+int io_register_device(const io_dev_info_t *dev_info);
 
 #endif  /* __IO_DRIVER_H__ */
diff --git a/include/drivers/io_fip.h b/include/drivers/io_fip.h
index 212570d..90b2fd0 100644
--- a/include/drivers/io_fip.h
+++ b/include/drivers/io_fip.h
@@ -33,6 +33,6 @@
 
 struct io_dev_connector;
 
-int register_io_dev_fip(struct io_dev_connector **dev_con);
+int register_io_dev_fip(const struct io_dev_connector **dev_con);
 
 #endif /* __IO_FIP_H__ */
diff --git a/include/drivers/io_memmap.h b/include/drivers/io_memmap.h
index 0e59ecb..7ee60fe 100644
--- a/include/drivers/io_memmap.h
+++ b/include/drivers/io_memmap.h
@@ -33,6 +33,6 @@
 
 struct io_dev_connector;
 
-int register_io_dev_memmap(struct io_dev_connector **dev_con);
+int register_io_dev_memmap(const struct io_dev_connector **dev_con);
 
 #endif /* __IO_MEMMAP_H__ */
diff --git a/include/drivers/io_semihosting.h b/include/drivers/io_semihosting.h
index eab290a..8902a6f 100644
--- a/include/drivers/io_semihosting.h
+++ b/include/drivers/io_semihosting.h
@@ -33,6 +33,6 @@
 
 struct io_dev_connector;
 
-int register_io_dev_sh(struct io_dev_connector **dev_con);
+int register_io_dev_sh(const struct io_dev_connector **dev_con);
 
 #endif /* __IO_SH_H__ */
diff --git a/include/lib/io_storage.h b/include/lib/io_storage.h
index b6c5f9f..ae1158c 100644
--- a/include/lib/io_storage.h
+++ b/include/lib/io_storage.h
@@ -31,6 +31,7 @@
 #ifndef __IO_H__
 #define __IO_H__
 
+#include <stdint.h>
 #include <stdio.h> /* For ssize_t */
 
 
@@ -58,13 +59,6 @@
 /* Connector type, providing a means of identifying a device to open */
 struct io_dev_connector;
 
-/* Device handle, providing a client with access to a specific device */
-typedef struct io_dev_info *io_dev_handle;
-
-/* IO handle, providing a client with access to a specific source of data from
- * a device */
-typedef struct io_entity *io_handle;
-
 
 /* File specification - used to refer to data on a device supporting file-like
  * entities */
@@ -77,7 +71,7 @@
 /* Block specification - used to refer to data on a device supporting
  * block-like entities */
 typedef struct io_block_spec {
-	unsigned long offset;
+	size_t offset;
 	size_t length;
 } io_block_spec_t;
 
@@ -96,33 +90,35 @@
 
 
 /* Open a connection to a device */
-int io_dev_open(struct io_dev_connector *dev_con, void *dev_spec,
-		io_dev_handle *dev_handle);
+int io_dev_open(const struct io_dev_connector *dev_con,
+		const uintptr_t dev_spec,
+		uintptr_t *dev_handle);
 
 
 /* Initialise a device explicitly - to permit lazy initialisation or
  * re-initialisation */
-int io_dev_init(io_dev_handle dev_handle, const void *init_params);
+int io_dev_init(uintptr_t dev_handle, const uintptr_t init_params);
 
 /* TODO: Consider whether an explicit "shutdown" API should be included */
 
 /* Close a connection to a device */
-int io_dev_close(io_dev_handle dev_handle);
+int io_dev_close(uintptr_t dev_handle);
 
 
 /* Synchronous operations */
-int io_open(io_dev_handle dev_handle, const void *spec, io_handle *handle);
+int io_open(uintptr_t dev_handle, const uintptr_t spec, uintptr_t *handle);
 
-int io_seek(io_handle handle, io_seek_mode_t mode, ssize_t offset);
+int io_seek(uintptr_t handle, io_seek_mode_t mode, ssize_t offset);
 
-int io_size(io_handle handle, size_t *length);
+int io_size(uintptr_t handle, size_t *length);
 
-int io_read(io_handle handle, void *buffer, size_t length, size_t *length_read);
+int io_read(uintptr_t handle, uintptr_t buffer, size_t length,
+		size_t *length_read);
 
-int io_write(io_handle handle, const void *buffer, size_t length,
+int io_write(uintptr_t handle, const uintptr_t buffer, size_t length,
 		size_t *length_written);
 
-int io_close(io_handle handle);
+int io_close(uintptr_t handle);
 
 
 #endif /* __IO_H__ */
diff --git a/include/lib/semihosting.h b/include/lib/semihosting.h
index 9d0b39f..b4eecc5 100644
--- a/include/lib/semihosting.h
+++ b/include/lib/semihosting.h
@@ -31,6 +31,7 @@
 #ifndef __SEMIHOSTING_H__
 #define __SEMIHOSTING_H__
 
+#include <stdint.h>
 #include <stdio.h> /* For ssize_t */
 
 
@@ -63,17 +64,17 @@
 long semihosting_connection_supported(void);
 long semihosting_file_open(const char *file_name, size_t mode);
 long semihosting_file_seek(long file_handle, ssize_t offset);
-long semihosting_file_read(long file_handle, size_t *length, void *buffer);
+long semihosting_file_read(long file_handle, size_t *length, uintptr_t buffer);
 long semihosting_file_write(long file_handle,
 			    size_t *length,
-			    const void *buffer);
+			    const uintptr_t buffer);
 long semihosting_file_close(long file_handle);
 long semihosting_file_length(long file_handle);
 long semihosting_system(char *command_line);
 long semihosting_get_flen(const char *file_name);
 long semihosting_download_file(const char *file_name,
 			       size_t buf_size,
-			       void *buf);
+			       uintptr_t buf);
 void semihosting_write_char(char character);
 void semihosting_write_string(char *string);
 char semihosting_read_char(void);