diff --git a/dspy/utils/usage_tracker.py b/dspy/utils/usage_tracker.py
index 1d3d13c638..e724e1de0e 100644
--- a/dspy/utils/usage_tracker.py
+++ b/dspy/utils/usage_tracker.py
@@ -45,7 +45,7 @@ def _merge_usage_entries(
             current_v = result.get(k)
             if isinstance(v, dict) or isinstance(current_v, dict):
                 result[k] = self._merge_usage_entries(current_v, v)
-            else:
+            elif current_v is not None or v is not None:
                 result[k] = (current_v or 0) + (v or 0)
         return result
 
diff --git a/tests/utils/test_usage_tracker.py b/tests/utils/test_usage_tracker.py
index 28e35e40ab..f3ae612738 100644
--- a/tests/utils/test_usage_tracker.py
+++ b/tests/utils/test_usage_tracker.py
@@ -190,6 +190,16 @@ def test_merge_usage_entries_with_none_values():
                 "prompt_tokens": 800,
                 "completion_tokens": 100,
                 "total_tokens": 900,
+                "prompt_tokens_details": None,
+                "completion_tokens_details": None,
+            },
+        },
+        {
+            "model": "gpt-4o-mini",
+            "usage": {
+                "prompt_tokens": 100,
+                "completion_tokens": 100,
+                "total_tokens": 200,
                 "prompt_tokens_details": {"cached_tokens": 50, "audio_tokens": 50},
                 "completion_tokens_details": None,
             },
@@ -216,9 +226,9 @@ def test_merge_usage_entries_with_none_values():
 
     total_usage = tracker.get_total_tokens()
 
-    assert total_usage["gpt-4o-mini"]["prompt_tokens"] == 2717
-    assert total_usage["gpt-4o-mini"]["completion_tokens"] == 246
-    assert total_usage["gpt-4o-mini"]["total_tokens"] == 2963
+    assert total_usage["gpt-4o-mini"]["prompt_tokens"] == 2817
+    assert total_usage["gpt-4o-mini"]["completion_tokens"] == 346
+    assert total_usage["gpt-4o-mini"]["total_tokens"] == 3163
     assert total_usage["gpt-4o-mini"]["prompt_tokens_details"]["cached_tokens"] == 50
     assert total_usage["gpt-4o-mini"]["prompt_tokens_details"]["audio_tokens"] == 50
     assert total_usage["gpt-4o-mini"]["completion_tokens_details"]["reasoning_tokens"] == 1