diff --git a/tensortrade/data/stream/feed.py b/tensortrade/data/stream/feed.py
index 0e7330503..def63d28f 100644
--- a/tensortrade/data/stream/feed.py
+++ b/tensortrade/data/stream/feed.py
@@ -99,14 +99,16 @@ def has_next(self) -> bool:
         return all(node.has_next() for node in self.process)
 
     def __add__(self, other):
-        if isinstance(other, DataFeed):
-            nodes = list(set(self.inputs + other.inputs))
-            feed = DataFeed(nodes)
+        if not isinstance(other, DataFeed):
+            raise TypeError(f'can only concatenate DataFeed (not "{type(other).__name__}") to DataFeed.')
 
-            for listener in self.listeners + other.listeners:
-                feed.attach(listener)
+        nodes = self.inputs + other.inputs
+        feed = DataFeed(nodes)
 
-            return feed
+        for listener in self.listeners + other.listeners:
+            feed.attach(listener)
+
+        return feed
 
     def reset(self):
         for node in self.process:
diff --git a/tensortrade/environments/trading_environment.py b/tensortrade/environments/trading_environment.py
index 4c0ed4fd8..61dcfaf7b 100644
--- a/tensortrade/environments/trading_environment.py
+++ b/tensortrade/environments/trading_environment.py
@@ -104,8 +104,8 @@ def compile(self):
 
         if not self.feed:
             self.feed = create_internal_feed(self.portfolio)
-
-        self.feed = self.feed + create_internal_feed(self.portfolio)
+        else:
+            self.feed = self.feed + create_internal_feed(self.portfolio)
 
         initial_obs = self.feed.next()
         n_features = len(initial_obs.keys()) if self.use_internal else len(self._external_keys)