diff --git a/haystack/pipelines/config.py b/haystack/pipelines/config.py
index 36ea6c1eb..8e1345a11 100644
--- a/haystack/pipelines/config.py
+++ b/haystack/pipelines/config.py
@@ -97,7 +97,10 @@ def read_pipeline_config_from_yaml(path: Path) -> Dict[str, Any]:
         return yaml.safe_load(stream)
 
 
-JSON_FIELDS = ["custom_query"]  # ElasticsearchDocumentStore.custom_query
+JSON_FIELDS = [
+    "custom_query",  # ElasticsearchDocumentStore.custom_query
+    "custom_mapping",  # ElasticsearchDocumentStore.custom_mapping
+]
 
 
 def validate_config_strings(pipeline_config: Any):
diff --git a/test/pipelines/test_pipeline.py b/test/pipelines/test_pipeline.py
index 0d3e09eab..2f29e8b62 100644
--- a/test/pipelines/test_pipeline.py
+++ b/test/pipelines/test_pipeline.py
@@ -687,6 +687,9 @@ def test_validate_pipeline_config_component_with_json_input_valid():
     validate_config_strings(
         {"components": [{"name": "test", "type": "test", "params": {"custom_query": '{"json-key": "json-value"}'}}]}
     )
+    validate_config_strings(
+        {"components": [{"name": "test", "type": "test", "params": {"custom_mapping": '{"json-key": "json-value"}'}}]}
+    )
 
 
 def test_validate_pipeline_config_component_with_json_input_invalid_key():