diff --git a/include/command.h b/include/command.h
index b9b5ec1..e900f97 100644
--- a/include/command.h
+++ b/include/command.h
@@ -117,7 +117,31 @@
 	defined(CONFIG_CMD_PCI) || \
 	defined(CONFIG_CMD_SETEXPR)
 #define CMD_DATA_SIZE
-extern int cmd_get_data_size(char* arg, int default_size);
+#define CMD_DATA_SIZE_ERR	(-1)
+#define CMD_DATA_SIZE_STR	(-2)
+
+/**
+ * cmd_get_data_size() - Get the data-size specifier from a command
+ *
+ * This reads a '.x' size specifier appended to a command. For example 'md.b'
+ * is the 'md' command with a '.b' specifier, meaning that the command should
+ * use bytes.
+ *
+ * Valid characters are:
+ *
+ *	b - byte
+ *	w - word (16 bits)
+ *	l - long (32 bits)
+ *	q - quad (64 bits)
+ *	s - string
+ *
+ * @arg: Pointers to the command to check. If a valid specifier is present it
+ *	will be the last character of the string, following a '.'
+ * @default_size: Default size to return if there is no specifier
+ * @return data size in bytes (1, 2, 4, 8) or CMD_DATA_SIZE_ERR for an invalid
+ *	character, or CMD_DATA_SIZE_STR for a string
+ */
+int cmd_get_data_size(char *arg, int default_size);
 #endif
 
 #ifdef CONFIG_CMD_BOOTD