diff --git a/interpreter/binary/encode.ml b/interpreter/binary/encode.ml
index aea746bcf..3dccb4243 100644
--- a/interpreter/binary/encode.ml
+++ b/interpreter/binary/encode.ml
@@ -593,9 +593,9 @@ let encode m =
       | SimdShift V128Op.(I64x2 ShrU) -> simd_op 0xcdl
       | SimdShift (_) -> assert false
 
-      | SimdBitmask V128Op.(I8x16 Bitmask) -> simd_op 0x64l
-      | SimdBitmask V128Op.(I16x8 Bitmask) -> simd_op 0x84l
-      | SimdBitmask V128Op.(I32x4 Bitmask) -> simd_op 0xa4l
+      | SimdBitmask Simd.I8x16 -> simd_op 0x64l
+      | SimdBitmask Simd.I16x8 -> simd_op 0x84l
+      | SimdBitmask Simd.I32x4 -> simd_op 0xa4l
       | SimdBitmask (_) -> assert false
 
       | _ -> assert false
diff --git a/interpreter/exec/eval_simd.ml b/interpreter/exec/eval_simd.ml
index 5214e53e7..624062919 100644
--- a/interpreter/exec/eval_simd.ml
+++ b/interpreter/exec/eval_simd.ml
@@ -215,11 +215,11 @@ module SimdOp (SXX : Simd.S) (Value : ValueType with type t = SXX.t) = struct
     | _ -> failwith "unimplemented shr_u"
     in fun v s -> to_value (f (of_value 1 v) (of_arg I32Value.of_value 2 s))
 
-  let bitmaskop (op : bitmaskop) v =
+  let bitmaskop (op : Simd.shape) v =
     let f = match op with
-    | I8x16 Bitmask -> SXX.I8x16.bitmask
-    | I16x8 Bitmask -> SXX.I16x8.bitmask
-    | I32x4 Bitmask -> SXX.I32x4.bitmask
+    | Simd.I8x16 -> SXX.I8x16.bitmask
+    | Simd.I16x8 -> SXX.I16x8.bitmask
+    | Simd.I32x4 -> SXX.I32x4.bitmask
     | _ -> assert false
     in I32 (f (of_value 1 v))
 
diff --git a/interpreter/exec/eval_simd.mli b/interpreter/exec/eval_simd.mli
index 89687f75d..3e47f8bb2 100644
--- a/interpreter/exec/eval_simd.mli
+++ b/interpreter/exec/eval_simd.mli
@@ -10,6 +10,6 @@ val cvtop : Ast.V128Op.cvtop -> value -> value
 
 val eval_ternop : Ast.V128Op.ternop -> value -> value -> value -> value
 val eval_shiftop : Ast.V128Op.shiftop -> value -> value -> value
-val eval_bitmaskop : Ast.V128Op.bitmaskop -> value -> value
+val eval_bitmaskop : Simd.shape -> value -> value
 val eval_extractop : Ast.V128Op.extractop -> value -> value
 val eval_replaceop : Ast.V128Op.replaceop -> value -> value -> value
diff --git a/interpreter/syntax/ast.ml b/interpreter/syntax/ast.ml
index a7ebf5e33..748b852ce 100644
--- a/interpreter/syntax/ast.ml
+++ b/interpreter/syntax/ast.ml
@@ -86,8 +86,6 @@ struct
   type replaceop = (int, int, int, int, int, int, int) v128op
   type shift = Shl | ShrS | ShrU
   type shiftop = (shift, shift, shift, shift, shift, shift, shift) v128op
-  type bitmask = Bitmask
-  type bitmaskop = (bitmask, bitmask, bitmask, bitmask, bitmask, bitmask, bitmask) v128op
 end
 
 module I32Op = IntOp
@@ -106,7 +104,6 @@ type replaceop = V128Op.replaceop
 (* Ternary operators only exist for V128 types for now *)
 type ternop = V128Op.ternop
 type shiftop = V128Op.shiftop
-type bitmaskop = V128Op.bitmaskop
 
 type 'a memop =
   {ty : value_type; align : int; offset : Memory.offset; sz : 'a option}
@@ -161,7 +158,7 @@ and instr' =
   | SimdExtract of extractop          (* extract lane from v128 value *)
   | SimdReplace of replaceop          (* replace lane of v128 value *)
   | SimdShift of shiftop              (* shifts for v128 value *)
-  | SimdBitmask of bitmaskop          (* bitmask for v128 value *)
+  | SimdBitmask of Simd.shape         (* bitmask for v128 value *)
 
 
 (* Globals & Functions *)
diff --git a/interpreter/syntax/operators.ml b/interpreter/syntax/operators.ml
index 2e0d008b0..34bffee9b 100644
--- a/interpreter/syntax/operators.ml
+++ b/interpreter/syntax/operators.ml
@@ -266,7 +266,7 @@ let i8x16_ge_s = Binary (V128 V128Op.(I8x16 GeS))
 let i8x16_ge_u = Binary (V128 V128Op.(I8x16 GeU))
 let i8x16_neg = Unary (V128 V128Op.(I8x16 Neg))
 let i8x16_any_true = Test (V128 V128Op.(I8x16 AnyTrue))
-let i8x16_bitmask = SimdBitmask V128Op.(I8x16 Bitmask)
+let i8x16_bitmask = SimdBitmask Simd.I8x16
 let i8x16_all_true = Test (V128 V128Op.(I8x16 AllTrue))
 let i8x16_narrow_i16x8_s = Binary (V128 V128Op.(I8x16 NarrowS))
 let i8x16_narrow_i16x8_u = Binary (V128 V128Op.(I8x16 NarrowU))
@@ -306,7 +306,7 @@ let i16x8_ge_s = Binary (V128 V128Op.(I16x8 GeS))
 let i16x8_ge_u = Binary (V128 V128Op.(I16x8 GeU))
 let i16x8_neg = Unary (V128 V128Op.(I16x8 Neg))
 let i16x8_any_true = Test (V128 V128Op.(I16x8 AnyTrue))
-let i16x8_bitmask = SimdBitmask V128Op.(I16x8 Bitmask)
+let i16x8_bitmask = SimdBitmask Simd.I16x8
 let i16x8_all_true = Test (V128 V128Op.(I16x8 AllTrue))
 let i16x8_narrow_i32x4_s = Binary (V128 V128Op.(I16x8 NarrowS))
 let i16x8_narrow_i32x4_u = Binary (V128 V128Op.(I16x8 NarrowU))
@@ -343,7 +343,7 @@ let i32x4_ge_u = Binary (V128 V128Op.(I32x4 GeU))
 let i32x4_abs = Unary (V128 V128Op.(I32x4 Abs))
 let i32x4_neg = Unary (V128 V128Op.(I32x4 Neg))
 let i32x4_any_true = Test (V128 V128Op.(I32x4 AnyTrue))
-let i32x4_bitmask = SimdBitmask V128Op.(I32x4 Bitmask)
+let i32x4_bitmask = SimdBitmask Simd.I32x4
 let i32x4_all_true = Test (V128 V128Op.(I32x4 AllTrue))
 let i32x4_widen_low_i16x8_s = Unary (V128 V128Op.(I32x4 WidenLowS))
 let i32x4_widen_high_i16x8_s = Unary (V128 V128Op.(I32x4 WidenHighS))
diff --git a/interpreter/text/arrange.ml b/interpreter/text/arrange.ml
index 416df398e..88c443e96 100644
--- a/interpreter/text/arrange.ml
+++ b/interpreter/text/arrange.ml
@@ -390,9 +390,9 @@ struct
     | _ -> assert false
 
   let bitmaskop = function
-    | I8x16 Bitmask -> "i8x16.bitmask"
-    | I16x8 Bitmask -> "i16x8.bitmask"
-    | I32x4 Bitmask -> "i32x4.bitmask"
+    | Simd.I8x16 -> "i8x16.bitmask"
+    | Simd.I16x8 -> "i16x8.bitmask"
+    | Simd.I32x4 -> "i32x4.bitmask"
     | _ -> assert false
 
 end