diff --git a/src/sentry/api/serializers/models/organization.py b/src/sentry/api/serializers/models/organization.py
index 97b422d1d2bdbf..57fe4a7765e958 100644
--- a/src/sentry/api/serializers/models/organization.py
+++ b/src/sentry/api/serializers/models/organization.py
@@ -695,7 +695,13 @@ def serialize(  # type: ignore[explicit-override, override]
         if sample_rate is not None:
             context["planSampleRate"] = sample_rate
 
-        desired_sample_rate, _ = get_org_sample_rate(org_id=obj.id, default_sample_rate=sample_rate)
+        if is_project_mode_sampling(obj):
+            desired_sample_rate = None
+        else:
+            desired_sample_rate, _ = get_org_sample_rate(
+                org_id=obj.id, default_sample_rate=sample_rate
+            )
+
         if desired_sample_rate is not None:
             context["desiredSampleRate"] = desired_sample_rate
 
diff --git a/tests/sentry/api/endpoints/test_organization_details.py b/tests/sentry/api/endpoints/test_organization_details.py
index 6172fd9cc8576a..f02afa413d9341 100644
--- a/tests/sentry/api/endpoints/test_organization_details.py
+++ b/tests/sentry/api/endpoints/test_organization_details.py
@@ -341,6 +341,8 @@ def test_is_dynamically_sampled_org_option(self):
         with self.feature({"organizations:dynamic-sampling-custom": True}):
             response = self.get_success_response(self.organization.slug)
             assert response.data["isDynamicallySampled"]
+            assert "planSampleRate" in response.data
+            assert "desiredSampleRate" in response.data
 
         self.organization.update_option(
             "sentry:sampling_mode", DynamicSamplingMode.ORGANIZATION.value
@@ -365,6 +367,8 @@ def test_is_dynamically_sampled_proj_option(self):
         with self.feature({"organizations:dynamic-sampling-custom": True}):
             response = self.get_success_response(self.organization.slug)
             assert response.data["isDynamicallySampled"]
+            assert "planSampleRate" not in response.data
+            assert "desiredSampleRate" not in response.data
 
     def test_dynamic_sampling_custom_target_sample_rate(self):
         with self.feature({"organizations:dynamic-sampling-custom": True}):