diff --git a/doc/README.dissector b/doc/README.dissector
index 45887b5c40..f074efaa0d 100644
--- a/doc/README.dissector
+++ b/doc/README.dissector
@@ -1009,6 +1009,14 @@ the same abbreviation. For instance, the following is valid:
 This way a filter expression can match a header field, irrespective of the
 representation of it in the specific protocol context. This is interesting
 for protocols with variable-width header fields.
+Note that the formats used must all belong to the same list as defined below:
+- FT_INT8, FT_INT16, FT_INT24 and FT_INT32
+- FT_UINT8, FT_UINT16, FT_UINT24, FT_UINT32, FT_IPXNET and FT_FRAMENUM
+- FT_UINT64 and FT_EUI64
+- FT_STRING, FT_STRINGZ and FT_UINT_STRING
+- FT_FLOAT and FT_DOUBLE
+- FT_BYTES, FT_UINT_BYTES, FT_AX25, FT_ETHER, FT_VINES, FT_OID and FT_REL_OID
+- FT_ABSOLUTE_TIME and FT_RELATIVE_TIME
 
 The HFILL macro at the end of the struct will set reasonable default values
 for internally used fields.