diff --git a/lib/bap_traces/bap_trace_event_types.ml b/lib/bap_traces/bap_trace_event_types.ml
index f923615abb..ed38e5400b 100644
--- a/lib/bap_traces/bap_trace_event_types.ml
+++ b/lib/bap_traces/bap_trace_event_types.ml
@@ -62,6 +62,10 @@ module Modload = struct
   } [@@deriving bin_io, compare, fields, sexp]
 end
 
+module Encoding = struct
+  type t = string [@@deriving bin_io, compare, sexp]
+end
+
 type 'a move = 'a Move.t [@@deriving bin_io, compare, sexp]
 type chunk = Chunk.t [@@deriving bin_io, compare, sexp]
 type syscall = Syscall.t [@@deriving bin_io, compare, sexp]
@@ -69,3 +73,4 @@ type exn = Exn.t [@@deriving bin_io, compare, sexp]
 type call = Call.t [@@deriving bin_io, compare, sexp]
 type return = Return.t [@@deriving bin_io, compare, sexp]
 type modload = Modload.t [@@deriving bin_io, compare, sexp]
+type encoding = Encoding.t [@@deriving bin_io, compare, sexp]
diff --git a/lib/bap_traces/bap_trace_events.ml b/lib/bap_traces/bap_trace_events.ml
index ecef5f5524..0dca6f4e10 100644
--- a/lib/bap_traces/bap_trace_events.ml
+++ b/lib/bap_traces/bap_trace_events.ml
@@ -104,6 +104,11 @@ module Pc_update = struct
   let pp = ppv "pc-update" Word.pp
 end
 
+module Encoding = struct
+  include Encoding
+  let pp = ppv "encoding" String.pp
+end
+
 let memory_load =
   Value.Tag.register (module Load)
     ~name:"memory-load"
@@ -168,3 +173,8 @@ let modload =
   Value.Tag.register (module Modload)
     ~name:"modload"
     ~uuid:"7f842d03-6c9f-4745-af39-002f468f7fc8"
+
+let encoding =
+  Value.Tag.register (module Encoding)
+    ~name:"encoding"
+    ~uuid:"f7ba0979-c3a9-4509-ba14-01faf577d478"
diff --git a/lib/bap_traces/bap_trace_events.mli b/lib/bap_traces/bap_trace_events.mli
index 829818149a..406eea5dff 100644
--- a/lib/bap_traces/bap_trace_events.mli
+++ b/lib/bap_traces/bap_trace_events.mli
@@ -65,3 +65,6 @@ val return : return tag
 
 (** represent an executable module being loaded *)
 val modload : modload tag
+
+(** the encoding used for future instructions has changed  *)
+val encoding : encoding tag
diff --git a/lib/bap_traces/bap_traces.mli b/lib/bap_traces/bap_traces.mli
index 83acc0138d..67c3d6ea6b 100644
--- a/lib/bap_traces/bap_traces.mli
+++ b/lib/bap_traces/bap_traces.mli
@@ -357,6 +357,13 @@ module Std : sig
     } [@@deriving bin_io, compare, fields, sexp]
   end
 
+
+  (** change of encoding of instructions (e.g. switch to thumb)  *)
+  module Encoding : sig
+    type t = string [@@deriving bin_io, compare, sexp]
+  end
+
+
   type 'a move = 'a Move.t [@@deriving bin_io, compare, sexp]
   type chunk = Chunk.t [@@deriving bin_io, compare, sexp]
   type syscall = Syscall.t [@@deriving bin_io, compare, sexp]
@@ -364,6 +371,7 @@ module Std : sig
   type call = Call.t [@@deriving bin_io, compare, sexp]
   type return = Return.t [@@deriving bin_io, compare, sexp]
   type modload = Modload.t [@@deriving bin_io, compare, sexp]
+  type encoding = Encoding.t [@@deriving bin_io, compare, sexp]
 
   (** Types of events.  *)
   module Event : sig
@@ -409,6 +417,9 @@ module Std : sig
 
     (** a module (shared library) is dynamically linked into a host program. *)
     val modload : modload tag
+
+    (** the encoding used for future instructions has changed  *)
+    val encoding : encoding tag
   end