diff --git a/.merlin b/.merlin
index 89aa7e875..f41d6e92d 100644
--- a/.merlin
+++ b/.merlin
@@ -64,6 +64,7 @@ B lib/bap_sema
 B lib/bap_strings
 B lib/bap_types
 B lib/bap_core_theory
+B lib/bap_traces
 B lib/graphlib
 B lib/monads
 B lib/ogre
diff --git a/lib/arm/arm_target.ml b/lib/arm/arm_target.ml
index f68e217d2..4fdfbd396 100644
--- a/lib/arm/arm_target.ml
+++ b/lib/arm/arm_target.ml
@@ -7,6 +7,7 @@ open KB.Syntax
 open Poly
 
 module CT = Theory
+module Mode = Bap_trace_event_types.Mode
 
 type r128 and r80 and r64 and r32 and r16 and r8
 
@@ -581,6 +582,11 @@ module Encodings = struct
     provide_primitive ()
 end
 
+module Modes = struct
+  let a32 = Mode.declare ~package:"arm" "a32"
+  let t32 = Mode.declare ~package:"arm" "t32"
+end
+
 let has_t32 label =
   KB.collect CT.Label.unit label >>= function
   | None -> !!false
@@ -639,15 +645,22 @@ let enable_pcode () =
   if is_arm t then pcode
   else Theory.Language.unknown
 
-let guess_encoding interworking label target =
+let guess_encoding interworking label target mode =
   if is_arm target then
     if is_64bit target then !!llvm_a64 else
     if is_thumb_only target
     then !!llvm_t32
-    else match interworking with
-      | Some true -> compute_encoding_from_symbol_table label
+    else
+      let from_mode_or fallback =
+        if Mode.equal mode Modes.t32 then !!llvm_t32
+        else if Mode.equal mode Modes.a32 then !!llvm_a32
+        else fallback () in
+      match interworking with
+      | Some true -> from_mode_or @@ fun () ->
+        compute_encoding_from_symbol_table label
       | Some false -> !!llvm_a32
-      | None -> has_t32 label >>= function
+      | None -> from_mode_or @@ fun () ->
+        has_t32 label >>= function
         | true -> compute_encoding_from_symbol_table label
         | false -> !!llvm_a32
   else !!CT.Language.unknown
@@ -658,8 +671,9 @@ let enable_llvm ?interworking () =
   register llvm_t32 "thumbv7" ~attrs:"+thumb2";
   register llvm_a64 "aarch64";
   KB.promise CT.Label.encoding @@ fun label ->
-  CT.Label.target label >>= guess_encoding interworking label
-
+  let* target = CT.Label.target label in
+  let* mode = KB.collect Mode.slot label in
+  guess_encoding interworking label target mode
 
 let load ?interworking ?(backend="llvm") () =
   enable_loader ();
diff --git a/lib/bap_traces/bap_trace_event_types.ml b/lib/bap_traces/bap_trace_event_types.ml
index f923615ab..3ae393e22 100644
--- a/lib/bap_traces/bap_trace_event_types.ml
+++ b/lib/bap_traces/bap_trace_event_types.ml
@@ -1,5 +1,9 @@
 open Bap.Std
 open Core_kernel
+open Bap_knowledge
+open Bap_core_theory
+
+module KB = Knowledge
 
 module Move = struct
   type 'a t = {
@@ -62,6 +66,11 @@ module Modload = struct
   } [@@deriving bin_io, compare, fields, sexp]
 end
 
+module Mode = struct
+  include KB.Enum.Make()
+  let slot = KB.Class.property ~package:"bap" Theory.Program.cls "mode" domain
+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 +78,4 @@ 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 mode = Mode.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 ecef5f552..6971e7cbf 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 Mode = struct
+  include Mode
+  let pp = ppv "mode" 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 mode =
+  Value.Tag.register (module Mode)
+    ~name:"mode"
+    ~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 829818149..1b141cd49 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 CPU mode used for future instructions has changed  *)
+val mode : mode tag
diff --git a/lib/bap_traces/bap_traces.ml b/lib/bap_traces/bap_traces.ml
index 1eeec2ee3..500c47eba 100644
--- a/lib/bap_traces/bap_traces.ml
+++ b/lib/bap_traces/bap_traces.ml
@@ -1,2 +1,3 @@
 module Unix = Caml_unix
 module Std = Bap_trace_std
+module KB = Bap_knowledge.Knowledge
diff --git a/lib/bap_traces/bap_traces.mli b/lib/bap_traces/bap_traces.mli
index 83acc0138..9a6e3763d 100644
--- a/lib/bap_traces/bap_traces.mli
+++ b/lib/bap_traces/bap_traces.mli
@@ -1,7 +1,11 @@
 open Core_kernel
 open Regular.Std
 open Bap.Std
+open Bap_knowledge
+open Bap_core_theory
+
 module Unix = Caml_unix
+module KB = Knowledge
 
 (** Traces of execution. *)
 module Std : sig
@@ -357,6 +361,14 @@ module Std : sig
     } [@@deriving bin_io, compare, fields, sexp]
   end
 
+
+  (** change of CPU mode (e.g. switch to thumb)  *)
+  module Mode : sig
+    include KB.Enum.S
+    val slot: (Theory.program, t) KB.slot
+  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 +376,7 @@ 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 mode = Mode.t [@@deriving bin_io, compare, sexp]
 
   (** Types of events.  *)
   module Event : sig
@@ -409,6 +422,9 @@ module Std : sig
 
     (** a module (shared library) is dynamically linked into a host program. *)
     val modload : modload tag
+
+    (** the CPU mode used for future instructions has changed  *)
+    val mode : mode tag
   end
 
 
diff --git a/oasis/arm b/oasis/arm
index 358452a6a..e29af8a04 100644
--- a/oasis/arm
+++ b/oasis/arm
@@ -8,7 +8,7 @@ Library "bap-arm"
  Build$:           flag(everything) || flag(arm)
  BuildDepends:     bap, core_kernel, ppx_bap, regular,
                    bap-core-theory, bap-knowledge, ogre,
-                   bitvec, bitvec-order, bap-primus
+                   bitvec, bitvec-order, bap-primus, bap-traces
  FindlibName:      bap-arm
  Modules:
                  ARM,
diff --git a/oasis/traces b/oasis/traces
index 94b79a073..06772b05c 100644
--- a/oasis/traces
+++ b/oasis/traces
@@ -18,7 +18,7 @@ Library traces
                    Bap_trace_std,
                    Bap_trace_traces,
                    Bap_trace
-  BuildDepends:    bap, core_kernel, uri, uuidm, regular, ppx_bap, core_kernel.caml_unix
+  BuildDepends:    bap, core_kernel, bap-core-theory, bap-knowledge, uri, uuidm, regular, ppx_bap, core_kernel.caml_unix
 
 Library traces_test
   Path:            lib_test/bap_traces