diff --git a/src/promptflow-tracing/promptflow/tracing/_trace.py b/src/promptflow-tracing/promptflow/tracing/_trace.py
index 735416550dc..0d4aecd40a2 100644
--- a/src/promptflow-tracing/promptflow/tracing/_trace.py
+++ b/src/promptflow-tracing/promptflow/tracing/_trace.py
@@ -143,6 +143,8 @@ def collect_openai_tokens_for_parent_span(self, span):
                     merged_tokens = {
                         key: self._span_id_to_tokens[parent_span_id].get(key, 0) + tokens.get(key, 0)
                         for key in set(self._span_id_to_tokens[parent_span_id]) | set(tokens)
+                        if isinstance(self._span_id_to_tokens[parent_span_id].get(key, 0), int)
+                        and isinstance(tokens.get(key, 0), int)
                     }
                     self._span_id_to_tokens[parent_span_id] = merged_tokens
                 else: