diff --git a/backend/apps/ifc_validation/tasks.py b/backend/apps/ifc_validation/tasks.py
index efff6e5..462c465 100644
--- a/backend/apps/ifc_validation/tasks.py
+++ b/backend/apps/ifc_validation/tasks.py
@@ -568,7 +568,15 @@ def schema_validation_subtask(self, prev_result, id, file_name, *args, **kwargs)
             task.mark_as_failed(err)
             raise
 
-        output = list(filter(None, proc.stdout.split("\n")))
+        # schema check returns either multiple JSON lines, or a single line message, or nothing.        
+        def is_schema_error(line):
+            try:
+                json.loads(line) # ignoring non-JSON messages
+            except ValueError:
+                return False
+            return True
+        
+        output = list(filter(is_schema_error, proc.stdout.split("\n")))
         # success = (len(output) == 0)
         # tfk: if we mark this task as failed we don't do the instance population either.
         # marking as failed should probably be reserved for blocking errors (prerequisites)