diff --git a/lib/pinc_bytecode/bytecode.ml b/lib/pinc_bytecode/bytecode.ml
index 2800615..385207b 100644
--- a/lib/pinc_bytecode/bytecode.ml
+++ b/lib/pinc_bytecode/bytecode.ml
@@ -1,20 +1,18 @@
 type t = {
-  instructions : Bytes.t;
+  instructions : Instruction.t Array.t;
   constants : Value.t Int32.Map.t;
 }
 
 let make ~instructions ~constants = { instructions; constants }
 
-let pp_instructions fmt instructions =
+let pp_instructions fmt =
   let offset = ref 0 in
-  while !offset < Bytes.length instructions do
-    let new_offset, t = Instruction.decode instructions !offset in
-    if !offset = 0 then
-      Format.fprintf fmt "%0.4i %a" !offset Instruction.pp t
-    else
-      Format.fprintf fmt "@;%0.4i %a" !offset Instruction.pp t;
-    offset := new_offset
-  done
+  Array.iter @@ fun instruction ->
+  if !offset = 0 then
+    Format.fprintf fmt "%0.4i %a" !offset Instruction.pp instruction
+  else
+    Format.fprintf fmt "@;%0.4i %a" !offset Instruction.pp instruction;
+  offset := !offset + Instruction.length instruction
 ;;
 
 let rec pp_value fmt = function
@@ -53,7 +51,7 @@ let pp fmt t =
     pp_constants fmt t.constants;
     Format.fprintf Format.std_formatter "@.");
 
-  if Bytes.length t.instructions > 0 then (
+  if Array.length t.instructions > 0 then (
     Format.fprintf Format.std_formatter "[INSTRUCTIONS]@.";
     Format.fprintf fmt "@[<v0>%a@]" pp_instructions t.instructions)
 ;;
@@ -69,8 +67,14 @@ let serialize t =
         Buffer.add_int32_be buf key;
         Value.serialize buf value)
   in
-  let () = Buffer.add_int32_be buf @@ Int32.of_int (Bytes.length t.instructions) in
-  let () = Buffer.add_bytes buf t.instructions in
+  let () = Buffer.add_int32_be buf @@ Int32.of_int (Array.length t.instructions) in
+  let () =
+    Array.iter
+      (fun instruction ->
+        let serialized = Instruction.to_bytes instruction in
+        Buffer.add_bytes buf serialized)
+      t.instructions
+  in
   Buffer.contents buf
 ;;
 
@@ -89,8 +93,12 @@ let deserialize str =
   in
   let instructions_length = Int32.to_int @@ Bytes.get_int32_be bytes !offset in
   offset := !offset + 4;
-  let instructions = Bytes.sub bytes !offset instructions_length in
-  offset := !offset + instructions_length;
+  let instructions =
+    Array.init instructions_length (fun _ ->
+        let new_offset, res = Instruction.decode bytes !offset in
+        offset := new_offset;
+        res)
+  in
   assert (!offset = Bytes.length bytes);
   make ~instructions ~constants
 ;;
diff --git a/lib/pinc_bytecode/instruction.ml b/lib/pinc_bytecode/instruction.ml
index 46bbabc..6aade5b 100644
--- a/lib/pinc_bytecode/instruction.ml
+++ b/lib/pinc_bytecode/instruction.ml
@@ -135,6 +135,8 @@ let operands_length = function
   | I_Debug_Print_Stack -> 0
 ;;
 
+let length t = 1 + operands_length t
+
 let decode bytes offset =
   let instruction = Bytes.get_uint8 bytes offset in
   let offset = offset + 1 in
diff --git a/lib/pinc_bytecode/value.ml b/lib/pinc_bytecode/value.ml
index ce0d21f..317aac0 100644
--- a/lib/pinc_bytecode/value.ml
+++ b/lib/pinc_bytecode/value.ml
@@ -19,7 +19,7 @@ and builtin_function = {
 and compiled_function = {
   num_locals : int;
   num_parameters : int;
-  instructions : Bytes.t;
+  instructions : Instruction.t Array.t;
 }
 
 and closure = {
@@ -110,11 +110,7 @@ let rec equal a b =
       Int.equal a.num_parameters b.num_parameters && Int.equal a.fn_index b.fn_index
   | _ -> false
 
-and equal_function a b =
-  Int.equal a.num_locals b.num_locals
-  && Int.equal a.num_parameters b.num_parameters
-  && Bytes.equal a.instructions b.instructions
-;;
+and equal_function a b = a == b
 
 let compare a b =
   match (a, b) with
@@ -185,8 +181,12 @@ and serialize_function buf f =
   Buffer.add_int8 buf 0x09;
   Buffer.add_int32_be buf @@ Int32.of_int num_locals;
   Buffer.add_int32_be buf @@ Int32.of_int num_parameters;
-  Buffer.add_int32_be buf @@ Int32.of_int (Bytes.length instructions);
-  Buffer.add_bytes buf instructions
+  Buffer.add_int32_be buf @@ Int32.of_int (Array.length instructions);
+  Array.iter
+    (fun instruction ->
+      let serialized = Instruction.to_bytes instruction in
+      Buffer.add_bytes buf serialized)
+    instructions
 
 and serialize_builtin_function buf f =
   let num_parameters = f.num_parameters in
@@ -265,8 +265,12 @@ and deserialize_function bytes offset =
   offset := !offset + 4;
   let instructions_length = Int32.to_int @@ Bytes.get_int32_be bytes !offset in
   offset := !offset + 4;
-  let instructions = Bytes.sub bytes !offset instructions_length in
-  offset := !offset + instructions_length;
+  let instructions =
+    Array.init instructions_length (fun _ ->
+        let new_offset, res = Instruction.decode bytes !offset in
+        offset := new_offset;
+        res)
+  in
   { num_locals; num_parameters; instructions }
 
 and deserialize_builtin_function bytes offset =
diff --git a/lib/pinc_compiler/compiler.ml b/lib/pinc_compiler/compiler.ml
index e0b5a35..a84b6d7 100644
--- a/lib/pinc_compiler/compiler.ml
+++ b/lib/pinc_compiler/compiler.ml
@@ -6,7 +6,7 @@ type emitted_instruction = {
 }
 
 type scope = {
-  instructions : Buffer.t;
+  instructions : Pinc_Bytecode.Instruction.t Dynarray.t;
   last_instruction : emitted_instruction;
   previous_instruction : emitted_instruction;
 }
@@ -58,13 +58,7 @@ let replace_instruction t offset instruction =
   match t.scopes with
   | [] -> assert false
   | scope :: _ ->
-      let current_instructions = Buffer.to_bytes scope.instructions in
-      let src = Pinc_Bytecode.Instruction.to_bytes instruction in
-      let srcoff = 0 in
-      let len = Bytes.length src in
-      Bytes.blit src srcoff current_instructions offset len;
-      Buffer.truncate scope.instructions 0;
-      Buffer.add_bytes scope.instructions current_instructions;
+      Dynarray.set scope.instructions offset instruction;
       t
 ;;
 
@@ -72,7 +66,7 @@ let remove_last_instruction t =
   match t.scopes with
   | [] -> assert false
   | scope :: scopes ->
-      Buffer.truncate scope.instructions scope.last_instruction.offset;
+      Dynarray.remove_last scope.instructions;
       let scope' = { scope with last_instruction = scope.previous_instruction } in
       { t with scopes = scope' :: scopes }
 ;;
@@ -85,7 +79,7 @@ let match_last_instruction t check =
 let add_scope t =
   let scope =
     {
-      instructions = Buffer.create 8;
+      instructions = Dynarray.create ();
       previous_instruction = empty_instruction;
       last_instruction = empty_instruction;
     }
@@ -119,8 +113,8 @@ let add_constant =
 
 let emit t opcode =
   let scope = current_scope t in
-  let offset = Buffer.length scope.instructions in
-  Buffer.add_bytes scope.instructions @@ Pinc_Bytecode.Instruction.to_bytes @@ opcode;
+  let offset = Dynarray.length scope.instructions in
+  Dynarray.add_last scope.instructions opcode;
   let t = set_last_instruction t offset opcode in
   t
 ;;
@@ -289,7 +283,7 @@ let rec compile_expr t (expr : Pinc_Types.Ast.expression) =
 
       let num_free_variables = List.length free_variables in
       let num_parameters = List.length parameters in
-      let instructions = Buffer.to_bytes scope.instructions in
+      let instructions = Dynarray.to_array @@ scope.instructions in
       let fn_addr, t =
         add_constant t
         @@ Pinc_Bytecode.Value.Function { num_locals; num_parameters; instructions }
@@ -429,7 +423,7 @@ and compile_conditional_expression t ~condition ~consequent ~alternate =
   (* Alternate *)
   let t = emit t (Pinc_Bytecode.Instruction.I_Jump 0xFFFFFFFl) in
   let jump_alternate_offset = last_instruction_offset t in
-  let jump_address = Int32.of_int (Buffer.length @@ current_instructions t) in
+  let jump_address = Int32.of_int (Dynarray.length @@ current_instructions t) in
   let t =
     replace_instruction t jump_consequent_offset
     @@ Pinc_Bytecode.Instruction.I_Jump_If_False jump_address
@@ -447,7 +441,7 @@ and compile_conditional_expression t ~condition ~consequent ~alternate =
         in
         t
   in
-  let jump_address = Int32.of_int (Buffer.length @@ current_instructions t) in
+  let jump_address = Int32.of_int (Dynarray.length @@ current_instructions t) in
   let t =
     replace_instruction t jump_alternate_offset
     @@ Pinc_Bytecode.Instruction.I_Jump jump_address
@@ -476,7 +470,7 @@ and compile_loop_expression t ~index ~iterator ~reverse:_ ~iterable ~body =
   let t = emit t @@ Pinc_Bytecode.Instruction.I_Length in
   let t = emit_set_symbol t length_symbol in
   (* Set Iterator *)
-  let jump_address = Int32.of_int (Buffer.length @@ current_instructions t) in
+  let jump_address = Int32.of_int (Dynarray.length @@ current_instructions t) in
   let t = emit_get_symbol t iterable_symbol in
   let t = emit_get_symbol t index_symbol in
   let t = emit t @@ Pinc_Bytecode.Instruction.I_Index in
@@ -536,7 +530,7 @@ let compile_declaration (decl : Pinc_Types.Ast.declaration) t =
 let compile (ast : Pinc_Types.Ast.t) =
   let scope =
     {
-      instructions = Buffer.create 8;
+      instructions = Dynarray.create ();
       previous_instruction = empty_instruction;
       last_instruction = empty_instruction;
     }
@@ -552,6 +546,6 @@ let compile (ast : Pinc_Types.Ast.t) =
 
   Pinc_Bytecode.Bytecode.serialize
   @@ Pinc_Bytecode.Bytecode.make
-       ~instructions:(Buffer.to_bytes @@ current_instructions t)
+       ~instructions:(Dynarray.to_array @@ current_instructions t)
        ~constants:t.constants
 ;;
diff --git a/lib/pinc_vm/vm.ml b/lib/pinc_vm/vm.ml
index ee92e6b..4502c2f 100644
--- a/lib/pinc_vm/vm.ml
+++ b/lib/pinc_vm/vm.ml
@@ -498,13 +498,11 @@ let execute_return t =
 let run t =
   while
     (current_frame t).instruction_pointer
-    < Bytes.length @@ Frame.instructions (current_frame t)
+    < Array.length @@ Frame.instructions (current_frame t)
   do
     let frame = current_frame t in
-    let new_ip, op =
-      Instruction.decode (Frame.instructions frame) frame.instruction_pointer
-    in
-    Frame.set_instruction_pointer frame new_ip;
+    let op = Array.get (Frame.instructions frame) frame.instruction_pointer in
+    Frame.set_instruction_pointer frame @@ succ frame.instruction_pointer;
     match op with
     | Instruction.I_Debug_Print_Stack -> execute_debug_print_stack t
     | Instruction.I_Pop -> execute_pop t
diff --git a/lib/pinc_vm/vm_frame.ml b/lib/pinc_vm/vm_frame.ml
index 108954e..044d36d 100644
--- a/lib/pinc_vm/vm_frame.ml
+++ b/lib/pinc_vm/vm_frame.ml
@@ -1,10 +1,19 @@
 type t = {
   base_pointer : int;
-  closure : Pinc_Bytecode.Value.closure;
   mutable instruction_pointer : int;
+  instructions : Pinc_Bytecode.Instruction.t Array.t;
+  closure : Pinc_Bytecode.Value.closure;
 }
 
-let make ~base_pointer ~closure = { base_pointer; closure; instruction_pointer = 0 }
-let instructions t = t.closure.fn.instructions
+let make ~base_pointer ~closure =
+  {
+    base_pointer;
+    closure;
+    instructions = closure.Pinc_Bytecode.Value.fn.instructions;
+    instruction_pointer = 0;
+  }
+;;
+
+let instructions t = t.instructions
 let free_variables t = t.closure.free_variables
 let set_instruction_pointer t i = t.instruction_pointer <- i
diff --git a/lib/pinc_vm/vm_stack.ml b/lib/pinc_vm/vm_stack.ml
index fe2bcb2..f337a16 100644
--- a/lib/pinc_vm/vm_stack.ml
+++ b/lib/pinc_vm/vm_stack.ml
@@ -25,32 +25,24 @@ let push t value =
   if t.stack_pointer > t.stack_size then
     raise_notrace Pinc_stack_overflow
   else (
-    t.stack.(t.stack_pointer) <- value;
+    Array.unsafe_set t.stack t.stack_pointer value;
     t.stack_pointer <- succ t.stack_pointer)
 ;;
 
 let pop t =
-  if t.stack_pointer == 0 then
-    assert false
-  else (
-    let value = t.stack.(t.stack_pointer - 1) in
-    t.stack_pointer <- pred t.stack_pointer;
-    value)
+  t.stack_pointer <- t.stack_pointer - 1;
+  Array.unsafe_get t.stack t.stack_pointer
 ;;
 
 let pop_n t n =
-  if t.stack_pointer < n then
-    assert false
-  else (
-    let elements = List.init n (fun index -> t.stack.(t.stack_pointer - n + index)) in
-    t.stack_pointer <- t.stack_pointer - n;
-    elements)
+  t.stack_pointer <- t.stack_pointer - n;
+  List.init n (fun index -> Array.unsafe_get t.stack (t.stack_pointer + index))
 ;;
 
 let nth t n =
   match t.stack_pointer - n with
   | 0 -> Pinc_Bytecode.Value.Null
-  | n -> t.stack.(n - 1)
+  | n -> Array.unsafe_get t.stack (n - 1)
 ;;
 
 let top t = nth t 0
diff --git a/test/vm/conditionals_instructions.t b/test/vm/conditionals_instructions.t
index e560241..e4a9bfa 100644
--- a/test/vm/conditionals_instructions.t
+++ b/test/vm/conditionals_instructions.t
@@ -1,9 +1,9 @@
   $ NO_COLOR="1" print_instructions . IfTrue
   [INSTRUCTIONS]
   0000 I_True
-  0001 I_Jump_If_False 0x0000000C (00000012)
+  0001 I_Jump_If_False 0x00000004 (00000004)
   0006 I_True
-  0007 I_Jump 0x0000000D (00000013)
+  0007 I_Jump 0x00000005 (00000005)
   0012 I_Null
   0013 I_Pop
 
@@ -11,9 +11,9 @@
   $ NO_COLOR="1" print_instructions . IfTrueElse
   [INSTRUCTIONS]
   0000 I_True
-  0001 I_Jump_If_False 0x0000000C (00000012)
+  0001 I_Jump_If_False 0x00000004 (00000004)
   0006 I_True
-  0007 I_Jump 0x0000000D (00000013)
+  0007 I_Jump 0x00000005 (00000005)
   0012 I_False
   0013 I_Pop
 
@@ -21,9 +21,9 @@
   $ NO_COLOR="1" print_instructions . IfFalse
   [INSTRUCTIONS]
   0000 I_False
-  0001 I_Jump_If_False 0x0000000C (00000012)
+  0001 I_Jump_If_False 0x00000004 (00000004)
   0006 I_True
-  0007 I_Jump 0x0000000D (00000013)
+  0007 I_Jump 0x00000005 (00000005)
   0012 I_Null
   0013 I_Pop
 
@@ -31,8 +31,8 @@
   $ NO_COLOR="1" print_instructions . IfFalseElse
   [INSTRUCTIONS]
   0000 I_False
-  0001 I_Jump_If_False 0x0000000C (00000012)
+  0001 I_Jump_If_False 0x00000004 (00000004)
   0006 I_True
-  0007 I_Jump 0x0000000D (00000013)
+  0007 I_Jump 0x00000005 (00000005)
   0012 I_False
   0013 I_Pop
diff --git a/test/vm/functions_instructions.t b/test/vm/functions_instructions.t
index 3cd4925..0c185bf 100644
--- a/test/vm/functions_instructions.t
+++ b/test/vm/functions_instructions.t
@@ -50,9 +50,9 @@
   0x00000001 (00000001) : 2
   0x00000002 (00000002) : <FUNCTION> [
     0000 I_True
-    0001 I_Jump_If_False 0x00000010 (00000016)
+    0001 I_Jump_If_False 0x00000004 (00000004)
     0006 I_Constant 0x00000000 (00000000)
-    0011 I_Jump 0x00000015 (00000021)
+    0011 I_Jump 0x00000005 (00000005)
     0016 I_Constant 0x00000001 (00000001)
     0021 I_Return
   ]
@@ -248,9 +248,9 @@
     0000 I_Get_Local 0x00000000 (00000000)
     0005 I_Constant 0x00000000 (00000000)
     0010 I_Less_Equal
-    0011 I_Jump_If_False 0x0000001A (00000026)
+    0011 I_Jump_If_False 0x00000006 (00000006)
     0016 I_Get_Local 0x00000000 (00000000)
-    0021 I_Jump 0x0000003D (00000061)
+    0021 I_Jump 0x00000011 (00000017)
     0026 I_Current_Closure
     0027 I_Get_Local 0x00000000 (00000000)
     0032 I_Constant 0x00000001 (00000001)
@@ -271,9 +271,9 @@
     0000 I_Get_Local 0x00000000 (00000000)
     0005 I_Constant 0x00000004 (00000004)
     0010 I_Less_Equal
-    0011 I_Jump_If_False 0x0000001A (00000026)
+    0011 I_Jump_If_False 0x00000006 (00000006)
     0016 I_Constant 0x00000005 (00000005)
-    0021 I_Jump 0x00000031 (00000049)
+    0021 I_Jump 0x0000000D (00000013)
     0026 I_Get_Local 0x00000000 (00000000)
     0031 I_Current_Closure
     0032 I_Get_Local 0x00000000 (00000000)
diff --git a/test/vm/loop_instructions.t b/test/vm/loop_instructions.t
index 2a9c6ad..70fc33f 100644
--- a/test/vm/loop_instructions.t
+++ b/test/vm/loop_instructions.t
@@ -39,7 +39,7 @@
   0111 I_Get_Global 0x00000003 (00000003)
   0116 I_Get_Global 0x00000002 (00000002)
   0121 I_Greater_Equal
-  0122 I_Jump_If_False 0x00000044 (00000068)
+  0122 I_Jump_If_False 0x00000010 (00000016)
   0127 I_Get_Global 0x00000002 (00000002)
   0132 I_Dynamic_Array
   0133 I_Pop