diff --git a/cosmos/dbt/selector.py b/cosmos/dbt/selector.py
index 9488f185f1..c641cb6551 100644
--- a/cosmos/dbt/selector.py
+++ b/cosmos/dbt/selector.py
@@ -169,7 +169,8 @@ def select_node_precursors(self, nodes: dict[str, DbtNode], root_id: str, select
                 new_generation: set[str] = set()
                 for node_id in previous_generation:
                     if node_id not in processed_nodes:
-                        new_generation.update(set(nodes[node_id].depends_on))
+                        if node_id in nodes:
+                            new_generation.update(set(nodes[node_id].depends_on))
                         processed_nodes.add(node_id)
                 selected_nodes.update(new_generation)
                 previous_generation = new_generation
@@ -548,6 +549,8 @@ def select_nodes_ids_by_intersection(self) -> set[str]:
         if self.config.graph_selectors:
             graph_selected_nodes = self.select_by_graph_operator()
             for node_id in graph_selected_nodes:
+                if node_id not in self.nodes:
+                    continue
                 node = self.nodes[node_id]
                 # Since the method below changes the tags of test nodes, it can lead to incorrect
                 # results during the application of graph selectors. Therefore, it is being run within
diff --git a/tests/dbt/test_selector.py b/tests/dbt/test_selector.py
index 9c5f5b208a..4644875236 100644
--- a/tests/dbt/test_selector.py
+++ b/tests/dbt/test_selector.py
@@ -507,6 +507,44 @@ def test_select_node_by_child_and_precursors_no_node():
     assert list(selected.keys()) == expected
 
 
+def test_select_nodes_by_precursors_with_external_dependency():
+    """Test that the + selector handles depends_on references to nodes not in the nodes dict.
+
+    When using dbt-loom for cross-project references, external nodes are filtered out during
+    manifest loading (they have no file path). However, local nodes may still have depends_on
+    entries pointing to these external nodes. The + selector should gracefully skip missing
+    nodes instead of raising a KeyError.
+    """
+    external_upstream_id = "model.upstream_project.external_model"
+
+    local_staging = DbtNode(
+        unique_id=f"{DbtResourceType.MODEL.value}.{SAMPLE_PROJ_PATH.stem}.local_staging",
+        resource_type=DbtResourceType.MODEL,
+        depends_on=[external_upstream_id],
+        file_path=SAMPLE_PROJ_PATH / "models/local_staging.sql",
+        tags=[],
+        config={},
+    )
+    local_marts = DbtNode(
+        unique_id=f"{DbtResourceType.MODEL.value}.{SAMPLE_PROJ_PATH.stem}.local_marts",
+        resource_type=DbtResourceType.MODEL,
+        depends_on=[local_staging.unique_id],
+        file_path=SAMPLE_PROJ_PATH / "models/local_marts.sql",
+        tags=[],
+        config={},
+    )
+
+    nodes_with_external_dep = {
+        local_staging.unique_id: local_staging,
+        local_marts.unique_id: local_marts,
+    }
+
+    selected = select_nodes(project_dir=SAMPLE_PROJ_PATH, nodes=nodes_with_external_dep, select=["+local_marts"])
+    assert local_marts.unique_id in selected
+    assert local_staging.unique_id in selected
+    assert external_upstream_id not in selected
+
+
 def test_select_node_by_descendants():
     selected = select_nodes(project_dir=SAMPLE_PROJ_PATH, nodes=sample_nodes, select=["grandparent+"])
     expected = [