diff --git a/smnp/ast/node/statement.py b/smnp/ast/node/statement.py
index eec2cff..3405c79 100644
--- a/smnp/ast/node/statement.py
+++ b/smnp/ast/node/statement.py
@@ -11,7 +11,7 @@ class StatementNode(Node):
         from smnp.ast.node.ret import ReturnNode
 
         return Parser.oneOf(
+            ExpressionNode.parse,
             BlockNode.parse,
             ReturnNode.parse,
-            ExpressionNode.parse
         )(input)
\ No newline at end of file
diff --git a/smnp/runtime/evaluators/map.py b/smnp/runtime/evaluators/map.py
index c3e2ca3..f1596f8 100644
--- a/smnp/runtime/evaluators/map.py
+++ b/smnp/runtime/evaluators/map.py
@@ -1,4 +1,6 @@
-from smnp.runtime.evaluator import Evaluator, evaluate
+from smnp.error.runtime import RuntimeException
+from smnp.runtime.evaluator import Evaluator
+from smnp.runtime.evaluators.expression import expressionEvaluator
 from smnp.type.model import Type
 
 
@@ -6,6 +8,12 @@ class MapEvaluator(Evaluator):
 
     @classmethod
     def evaluator(cls, node, environment):
-        keys = [ evaluate(entry.key, environment).value for entry in node.children ]
-        values = [ evaluate(entry.value, environment).value for entry in node.children ]
-        return Type.map(dict(zip(keys, values)))
\ No newline at end of file
+        map = {}
+        exprEvaluator = expressionEvaluator(doAssert=True)
+        for entry in node.children:
+            key = exprEvaluator(entry.key, environment).value
+            if key in map:
+                raise RuntimeException(f"Duplicated key '{key.stringify()}' found in map", entry.pos)
+            map[key] = exprEvaluator(entry.value, environment).value
+
+        return Type.map(map)
\ No newline at end of file