diff --git a/haystack/pipeline.py b/haystack/pipeline.py
index bb9abde49..c1560395b 100644
--- a/haystack/pipeline.py
+++ b/haystack/pipeline.py
@@ -24,7 +24,7 @@ from haystack.graph_retriever.base import BaseGraphRetriever
 logger = logging.getLogger(__name__)
 
 
-class Pipeline(ABC):
+class Pipeline:
     """
     Pipeline brings together building blocks to build a complex search pipeline with Haystack & user-defined components.
 
@@ -65,6 +65,9 @@ class Pipeline(ABC):
         self.graph.add_node(name, component=component, inputs=inputs)
 
         if len(self.graph.nodes) == 2:  # first node added; connect with Root
+            assert len(inputs) == 1 and inputs[0].split(".")[0] == self.root_node_id, \
+                f"The '{name}' node can only input from {self.root_node_id}. " \
+                f"Set the 'inputs' parameter to ['{self.root_node_id}']"
             self.graph.add_edge(self.root_node_id, name, label="output_1")
             return
 
diff --git a/test/test_pipeline.py b/test/test_pipeline.py
index 41a6bb951..8a8d44634 100644
--- a/test/test_pipeline.py
+++ b/test/test_pipeline.py
@@ -29,7 +29,9 @@ def test_load_yaml(document_store_with_docs):
 
 @pytest.mark.slow
 @pytest.mark.elasticsearch
-@pytest.mark.parametrize("retriever_with_docs", ["elasticsearch"], indirect=True)
+@pytest.mark.parametrize(
+    "retriever_with_docs, document_store_with_docs", [("elasticsearch", "elasticsearch")], indirect=True
+)
 def test_graph_creation(reader, retriever_with_docs, document_store_with_docs):
     pipeline = Pipeline()
     pipeline.add_node(name="ES", component=retriever_with_docs, inputs=["Query"])
@@ -43,6 +45,10 @@ def test_graph_creation(reader, retriever_with_docs, document_store_with_docs):
     with pytest.raises(Exception):
         pipeline.add_node(name="Reader", component=retriever_with_docs, inputs=["InvalidNode"])
 
+    with pytest.raises(Exception):
+        pipeline = Pipeline()
+        pipeline.add_node(name="ES", component=retriever_with_docs, inputs=["InvalidNode"])
+
 
 @pytest.mark.slow
 @pytest.mark.elasticsearch