diff --git a/canopen/pdo/__init__.py b/canopen/pdo/__init__.py
index b749dfee..a48831ea 100644
--- a/canopen/pdo/__init__.py
+++ b/canopen/pdo/__init__.py
@@ -19,6 +19,35 @@
 logger = logging.getLogger(__name__)
 
 
+class _CombinedPdoMaps(Mapping[int, PdoMap]):
+    """Combine RPDO and TPDO :class:`PdoMaps` without dummy zero offsets.
+
+    Avoids ``PdoMaps(0, 0, …)`` where ``__getitem__`` fallbacks would alias
+    ``key`` to ``key + 1`` (see discussion on PR #613).
+    """
+
+    def __init__(self, rx: PdoMaps, tx: PdoMaps):
+        self.rx = rx
+        self.tx = tx
+
+    def __getitem__(self, key: int) -> PdoMap:
+        for maps in (self.rx, self.tx):
+            try:
+                return maps[key]
+            except KeyError:
+                continue
+        raise KeyError(key)
+
+    def __iter__(self) -> Iterator[int]:
+        return itertools.chain(
+            (self.rx.map_offset + i - 1 for i in self.rx),
+            (self.tx.map_offset + i - 1 for i in self.tx),
+        )
+
+    def __len__(self) -> int:
+        return len(self.rx) + len(self.tx)
+
+
 class PDO(PdoBase):
     """PDO Class for backwards compatibility.