diff --git a/native_exec/simple_x64.py b/native_exec/simple_x64.py
index b2fc56c..d3c2188 100644
--- a/native_exec/simple_x64.py
+++ b/native_exec/simple_x64.py
@@ -770,7 +770,7 @@ class MultipleInstr(object):
         # Change DelayedJump to LabeledJump ?
         if isinstance(instruction, DelayedJump):
             return self.add_delayed_jump(instruction)
-        if isinstance(instruction, Instruction):
+        if isinstance(instruction, (Instruction, Prefix)):
             self.instrs[self.size] = instruction
             self.size += len(instruction.get_code())
             return
diff --git a/native_exec/simple_x86.py b/native_exec/simple_x86.py
index ac2292f..51e9c83 100644
--- a/native_exec/simple_x86.py
+++ b/native_exec/simple_x86.py
@@ -660,7 +660,7 @@ class MultipleInstr(object):
         # Change DelayedJump to LabeledJump ?
         if isinstance(instruction, DelayedJump):
             return self.add_delayed_jump(instruction)
-        if isinstance(instruction, Instruction):
+        if isinstance(instruction, (Instruction, Prefix)):
             self.instrs[self.size] = instruction
             self.size += len(instruction.get_code())
             return
diff --git a/native_exec/test_simple_x64.py b/native_exec/test_simple_x64.py
index 1be0236..e1e55c3 100644
--- a/native_exec/test_simple_x64.py
+++ b/native_exec/test_simple_x64.py
@@ -111,4 +111,11 @@ TestInstr(Cpuid)()
 
 
 TestInstr(Xchg)('RAX', 'RSP')
-assert Xchg('RAX', 'RCX').get_code() == Xchg('RCX', 'RAX').get_code()
\ No newline at end of file
+assert Xchg('RAX', 'RCX').get_code() == Xchg('RCX', 'RAX').get_code()
+
+code = MultipleInstr()
+code += Nop()
+code += Rep + Nop()
+code += Ret()
+print(repr(code.get_code()))
+assert code.get_code() == "\x90\xf3\x90\xc3"
\ No newline at end of file
diff --git a/native_exec/test_simple_x86.py b/native_exec/test_simple_x86.py
index 90f87e7..beb1c7d 100644
--- a/native_exec/test_simple_x86.py
+++ b/native_exec/test_simple_x86.py
@@ -117,3 +117,11 @@ TestInstr(Movsd, expected_result='movsd dword ptr es:[edi], dword ptr [esi]')()
 
 TestInstr(Xchg)('EAX', 'ESP')
 assert Xchg('EAX', 'ECX').get_code() == Xchg('ECX', 'EAX').get_code()
+
+
+code = MultipleInstr()
+code += Nop()
+code += Rep + Nop()
+code += Ret()
+print(repr(code.get_code()))
+assert code.get_code() == "\x90\xf3\x90\xc3"