diff --git a/docs/reference.rst b/docs/reference.rst
index d67499e..64f813d 100644
--- a/docs/reference.rst
+++ b/docs/reference.rst
@@ -13,9 +13,9 @@ pb_type_t
 ---------
 Defines the encoder/decoder behaviour that should be used for a field. ::
 
-    typedef enum { ... } pb_type_t;
+    typedef uint8_t pb_type_t;
 
-The low-order byte of the enumeration values defines the function that can be used for encoding and decoding the field data:
+The low-order nibble of the enumeration values defines the function that can be used for encoding and decoding the field data:
 
 ==================== ===== ================================================
 LTYPE identifier     Value Storage format
@@ -28,7 +28,7 @@ PB_LTYPE_STRING      0x04  Null-terminated string.
 PB_LTYPE_SUBMESSAGE  0x05  Submessage structure.
 ==================== ===== ================================================
 
-The high-order byte defines whether the field is required, optional, repeated or callback:
+The high-order nibble defines whether the field is required, optional, repeated or callback:
 
 ==================== ===== ================================================
 HTYPE identifier     Value Field handling
diff --git a/pb.h b/pb.h
index cd9c75d..eef303a 100644
--- a/pb.h
+++ b/pb.h
@@ -27,56 +27,56 @@
  * SINT* is different, though, because it is zig-zag coded.
  */
 
-typedef enum {
-    /************************
-     * Field contents types *
-     ************************/
-    
-    /* Numeric types */
-    PB_LTYPE_VARINT = 0x00, /* int32, uint32, int64, uint64, bool, enum */
-    PB_LTYPE_SVARINT = 0x01, /* sint32, sint64 */
-    PB_LTYPE_FIXED32 = 0x02, /* fixed32, sfixed32, float */
-    PB_LTYPE_FIXED64 = 0x03, /* fixed64, sfixed64, double */
-    
-    /* Marker for last packable field type. */
-    PB_LTYPE_LAST_PACKABLE = 0x03,
-    
-    /* Byte array with pre-allocated buffer.
-     * data_size is the length of the allocated PB_BYTES_ARRAY structure. */
-    PB_LTYPE_BYTES = 0x04,
-    
-    /* String with pre-allocated buffer.
-     * data_size is the maximum length. */
-    PB_LTYPE_STRING = 0x05,
-    
-    /* Submessage
-     * submsg_fields is pointer to field descriptions */
-    PB_LTYPE_SUBMESSAGE = 0x06,
-    
-    /* Number of declared LTYPES */
-    PB_LTYPES_COUNT = 7,
-    
-    /******************
-     * Modifier flags *
-     ******************/
-    
-    /* Just the basic, write data at data_offset */
-    PB_HTYPE_REQUIRED = 0x00,
-    
-    /* Write true at size_offset */
-    PB_HTYPE_OPTIONAL = 0x10,
-    
-    /* Read to pre-allocated array
-     * Maximum number of entries is array_size,
-     * actual number is stored at size_offset */
-    PB_HTYPE_ARRAY = 0x20,
-    
-    /* Works for all required/optional/repeated fields.
-     * data_offset points to pb_callback_t structure.
-     * LTYPE should be 0 (it is ignored, but sometimes
-     * used to speculatively index an array). */
-    PB_HTYPE_CALLBACK = 0x30
-} pb_packed pb_type_t;
+/************************
+ * Field contents types *
+ ************************/
+
+typedef uint8_t pb_type_t;
+
+/* Numeric types */
+#define PB_LTYPE_VARINT 0x00 /* int32, uint32, int64, uint64, bool, enum */
+#define PB_LTYPE_SVARINT 0x01 /* sint32, sint64 */
+#define PB_LTYPE_FIXED32 0x02 /* fixed32, sfixed32, float */
+#define PB_LTYPE_FIXED64 0x03 /* fixed64, sfixed64, double */
+
+/* Marker for last packable field type. */
+#define PB_LTYPE_LAST_PACKABLE 0x03
+
+/* Byte array with pre-allocated buffer.
+ * data_size is the length of the allocated PB_BYTES_ARRAY structure. */
+#define PB_LTYPE_BYTES 0x04
+
+/* String with pre-allocated buffer.
+ * data_size is the maximum length. */
+#define PB_LTYPE_STRING 0x05
+
+/* Submessage
+ * submsg_fields is pointer to field descriptions */
+#define PB_LTYPE_SUBMESSAGE 0x06
+
+/* Number of declared LTYPES */
+#define PB_LTYPES_COUNT 7
+
+/******************
+ * Modifier flags *
+ ******************/
+
+/* Just the basic, write data at data_offset */
+#define PB_HTYPE_REQUIRED 0x00
+
+/* Write true at size_offset */
+#define PB_HTYPE_OPTIONAL 0x10
+
+/* Read to pre-allocated array
+ * Maximum number of entries is array_size,
+ * actual number is stored at size_offset */
+#define PB_HTYPE_ARRAY 0x20
+
+/* Works for all required/optional/repeated fields.
+ * data_offset points to pb_callback_t structure.
+ * LTYPE should be 0 (it is ignored, but sometimes
+ * used to speculatively index an array). */
+#define PB_HTYPE_CALLBACK 0x30
 
 #define PB_HTYPE(x) ((x) & 0xF0)
 #define PB_LTYPE(x) ((x) & 0x0F)