diff --git a/lib/galaxy/tools/actions/__init__.py b/lib/galaxy/tools/actions/__init__.py
index 8403e0137bb..8afad126269 100644
--- a/lib/galaxy/tools/actions/__init__.py
+++ b/lib/galaxy/tools/actions/__init__.py
@@ -17,8 +17,12 @@ from typing import (
 from packaging.version import Version
 
 from galaxy import model
-from galaxy.exceptions import ItemAccessibilityException
+from galaxy.exceptions import (
+    ItemAccessibilityException,
+    RequestParameterInvalidException,
+)
 from galaxy.job_execution.actions.post import ActionBox
+from galaxy.managers.context import ProvidesHistoryContext
 from galaxy.model import (
     HistoryDatasetAssociation,
     Job,
@@ -98,7 +102,7 @@ class DefaultToolAction(ToolAction):
         self,
         tool,
         param_values,
-        trans,
+        trans: ProvidesHistoryContext,
         history,
         current_user_roles=None,
         dataset_collection_elements=None,
@@ -256,6 +260,10 @@ class DefaultToolAction(ToolAction):
                 for ext in extensions:
                     if ext:
                         datatype = trans.app.datatypes_registry.get_datatype_by_extension(ext)
+                        if not datatype:
+                            raise RequestParameterInvalidException(
+                                f"Extension '{ext}' unknown, cannot use dataset collection as input"
+                            )
                         if not datatype.matches_any(input.formats):
                             conversion_required = True
                             break