diff --git a/c_gen/templates/loci_int.h b/c_gen/templates/loci_int.h
index 9907349..eb1c923 100644
--- a/c_gen/templates/loci_int.h
+++ b/c_gen/templates/loci_int.h
@@ -241,13 +241,16 @@
  * @param obj An object of type of_packet_in_t
  *
  * Get length of preceding match object and add to fixed length
- * Applies only to version 1.2 and 1.3
- * The +2 comes from the 2 bytes of padding between the match and packet data.
+ * Applies only to version 1.2+
+ * There are 2 bytes of padding between the match and data. The
+ * _OFFSET_FOLLOWING_MATCH_V3 macro assumes the match is at the end of the
+ * fixed length, so we need to subtract 2 from the fixed length we pass and
+ * then add 2 to the resulting offset.
  */
 
 #define _PACKET_IN_DATA_OFFSET(obj) \
     (_OFFSET_FOLLOWING_MATCH_V3((obj), (obj)->version == OF_VERSION_1_2 ? \
-${packet_in} : ${packet_in_1_3}) + 2)
+(${packet_in} - 2) : (${packet_in_1_3} - 2)) + 2)
 
 /**
  * Macro to calculate variable offset of data (packet) member in packet_out