diff --git a/mythril/laser/ethereum/instructions.py b/mythril/laser/ethereum/instructions.py
index 0965c8ce..ac6033da 100644
--- a/mythril/laser/ethereum/instructions.py
+++ b/mythril/laser/ethereum/instructions.py
@@ -939,9 +939,16 @@ class Instruction:
 
             return [global_state]
 
+        try:
+            memory_out_offset = util.get_concrete_int(memory_out_offset) if isinstance(memory_out_offset, ExprRef) else memory_out_offset
+            memory_out_size = util.get_concrete_int(memory_out_size) if isinstance(memory_out_size, ExprRef) else memory_out_size
+        except AttributeError:
+            global_state.mstate.stack.append(BitVec("retval_" + str(instr['address']), 256))
+            return [global_state]
+
         # Copy memory
-        global_state.mstate.mem_extend(memory_out_offset, min(memory_out_size.as_long(), len(global_state.last_return_data)))
-        for i in range(min(memory_out_size.as_long(), len(global_state.last_return_data))):
+        global_state.mstate.mem_extend(memory_out_offset, min(memory_out_size, len(global_state.last_return_data)))
+        for i in range(min(memory_out_size, len(global_state.last_return_data))):
             global_state.mstate.memory[i + memory_out_offset] = global_state.last_return_data[i]
 
         # Put return value on stack