diff --git a/lib/galaxy/tools/parameters/basic.py b/lib/galaxy/tools/parameters/basic.py
index a60053b711d..65d2a7c8767 100644
--- a/lib/galaxy/tools/parameters/basic.py
+++ b/lib/galaxy/tools/parameters/basic.py
@@ -2275,7 +2275,23 @@ class DataToolParameter(BaseDataToolParameter):
             if len(rval) > 1:
                 raise ParameterValueError("more than one dataset supplied to single input dataset parameter", self.name)
             if len(rval) > 0:
-                return rval[0]
+                single_value = rval[0]
+                if isinstance(single_value, HistoryDatasetCollectionAssociation):
+                    # A non-multiple data parameter cannot reduce a dataset
+                    # collection. Without this check the HDCA is silently
+                    # accepted here, then ``collect_input_dataset_collections``
+                    # rewrites the state to a list of the collection's HDAs and
+                    # ``wrap_values`` later crashes with a raw ``TypeError``
+                    # (https://github.com/galaxyproject/galaxy/issues/22401).
+                    # Map-over remains supported via ``{"batch": true, ...}``,
+                    # which is expanded to per-element jobs before reaching
+                    # ``from_json``.
+                    raise ParameterValueError(
+                        "dataset collection supplied to single input dataset parameter; "
+                        "to run the tool over each element of the collection, use the map-over option",
+                        self.name,
+                    )
+                return single_value
             else:
                 raise ParameterValueError("invalid dataset supplied to single input dataset parameter", self.name)
         return rval
diff --git a/lib/galaxy_test/api/test_tools.py b/lib/galaxy_test/api/test_tools.py
index 1f661ffcbb5..5c69b534585 100644
--- a/lib/galaxy_test/api/test_tools.py
+++ b/lib/galaxy_test/api/test_tools.py
@@ -2510,6 +2510,22 @@ class TestToolsApi(ApiTestCase, TestsTools):
         collection.assert_has_dataset_element("forward").with_contents_stripped("forward")
         collection.assert_has_dataset_element("reverse").with_contents_stripped("reverse")
 
+    @skip_without_tool("identifier_in_conditional")
+    def test_hdca_rejected_for_single_data_param_in_conditional(self, history_id):
+        # Regression test for https://github.com/galaxyproject/galaxy/issues/22401 .
+        # Submitting a paired collection (no batch wrapper) to a non-multiple
+        # ``data`` parameter is invalid and must produce a 400 client error,
+        # not a 500 from a TypeError raised inside ``wrap_values``. Map-over is
+        # still supported via ``{"batch": True, "values": [...]}``, exercised
+        # by ``test_identifier_map_over_input_in_conditional``.
+        hdca_id = self._build_pair(history_id, ["123", "456"])
+        inputs = {
+            "outer_cond|multi_input": False,
+            "outer_cond|input1": {"src": "hdca", "id": hdca_id},
+        }
+        response = self._run("identifier_in_conditional", history_id, inputs)
+        self._assert_status_code_is(response, 400)
+
     @skip_without_tool("identifier_multiple_in_conditional")
     def test_identifier_multiple_reduce_in_conditional(self, history_id):
         hdca_id = self._build_pair(history_id, ["123", "456"])