Add an explicit PLIST_FORMAT_NONE value
diff --git a/include/plist/plist.h b/include/plist/plist.h
index 7605975..47eda51 100644
--- a/include/plist/plist.h
+++ b/include/plist/plist.h
@@ -158,6 +158,7 @@
      */
     typedef enum
     {
+        PLIST_FORMAT_NONE    = 0,  /**< No format */
         PLIST_FORMAT_XML     = 1,  /**< XML format */
         PLIST_FORMAT_BINARY  = 2,  /**< bplist00 format */
         PLIST_FORMAT_JSON    = 3,  /**< JSON format */
diff --git a/src/plist.c b/src/plist.c
index 677e398..ccb7359 100644
--- a/src/plist.c
+++ b/src/plist.c
@@ -207,8 +207,8 @@
     if (!plist_data || length == 0) {
         return PLIST_ERR_INVALID_ARG;
     }
-    plist_format_t fmt = 0;
-    if (format) *format = 0;
+    plist_format_t fmt = PLIST_FORMAT_NONE;
+    if (format) *format = PLIST_FORMAT_NONE;
     if (plist_is_binary(plist_data, length)) {
         res = plist_from_bin(plist_data, length, plist);
         fmt = PLIST_FORMAT_BINARY;