diff --git a/mythril/laser/ethereum/instructions.py b/mythril/laser/ethereum/instructions.py
index da70f2be..7ca8b4df 100644
--- a/mythril/laser/ethereum/instructions.py
+++ b/mythril/laser/ethereum/instructions.py
@@ -553,7 +553,7 @@ class Instruction:
                     + str(hash(simplify(exponent)))
                     + ")",
                     256,
-                    base.annotations + exponent.annotations,
+                    base.annotations.union(exponent.annotations),
                 )
             )  # Hash is used because str(symbol) takes a long time to be converted to a string
         else:
@@ -925,7 +925,7 @@ class Instruction:
 
         if data.symbolic:
 
-            annotations = set()
+            annotations = set()  # Type: Set
 
             for b in state.memory[index : index + length]:
                 if isinstance(b, BitVec):
diff --git a/mythril/laser/smt/__init__.py b/mythril/laser/smt/__init__.py
index 5a3f1ca1..407f6565 100644
--- a/mythril/laser/smt/__init__.py
+++ b/mythril/laser/smt/__init__.py
@@ -22,11 +22,11 @@ from mythril.laser.smt.array import K, Array, BaseArray
 from mythril.laser.smt.solver import Solver, Optimize, SolverStatistics
 from mythril.laser.smt.model import Model
 
-from typing import Union, Any, Optional, List, TypeVar, Generic
+from typing import Union, Any, Optional, Set, TypeVar, Generic
 import z3
 
 
-Annotations = Optional[List[Any]]
+Annotations = Optional[Set[Any]]
 T = TypeVar("T", bound=Union[bool.Bool, z3.BoolRef])
 U = TypeVar("U", bound=Union[BitVec, z3.BitVecRef])