diff --git a/src/interpreter/resolver.py b/src/interpreter/resolver.py
index 002ff13..abcb179 100644
--- a/src/interpreter/resolver.py
+++ b/src/interpreter/resolver.py
@@ -31,7 +31,10 @@ class Resolver(Expr.Visitor[None], Stmt.Visitor[None]):
     def declare(self, name: Token) -> None:
         if len(self.scopes) == 0:
             return
-        self.scopes[-1][name.lexeme] = False
+        scope: dict[str, bool] = self.scopes[-1]
+        if name.lexeme in scope:
+            Pebble.token_error(name, "A variable with this name is already declared in this scope.")
+        scope[name.lexeme] = False
 
     def define(self, name: Token) -> None:
         if len(self.scopes) == 0: