diff --git a/src/google/adk/planners/plan_re_act_planner.py b/src/google/adk/planners/plan_re_act_planner.py
index dab3a1fecb..48ca41bb21 100644
--- a/src/google/adk/planners/plan_re_act_planner.py
+++ b/src/google/adk/planners/plan_re_act_planner.py
@@ -71,7 +71,7 @@ def process_planning_response(
       # Split the response into reasoning and final answer parts.
       self._handle_non_function_call_parts(response_parts[i], preserved_parts)
 
-    if first_fc_part_index > 0:
+    if first_fc_part_index >= 0:
       j = first_fc_part_index + 1
       while j < len(response_parts):
         if response_parts[j].function_call:
diff --git a/tests/unittests/planners/__init__.py b/tests/unittests/planners/__init__.py
new file mode 100644
index 0000000000..58d482ea38
--- /dev/null
+++ b/tests/unittests/planners/__init__.py
@@ -0,0 +1,13 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
diff --git a/tests/unittests/planners/test_plan_re_act_planner.py b/tests/unittests/planners/test_plan_re_act_planner.py
new file mode 100644
index 0000000000..ccafdf48a9
--- /dev/null
+++ b/tests/unittests/planners/test_plan_re_act_planner.py
@@ -0,0 +1,58 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tests for PlanReActPlanner.process_planning_response."""
+
+from google.adk.planners.plan_re_act_planner import PlanReActPlanner
+from google.genai import types
+
+
+def _function_call_names(parts):
+  return [p.function_call.name for p in parts if p.function_call]
+
+
+def test_preserves_all_leading_parallel_function_calls():
+  """Parallel function calls at the start of the response must all survive.
+
+  Regression test: the trailing-group guard used ``> 0``, so when the first
+  part was a function call (index 0) the loop that collects the rest of the
+  parallel call group never ran and every call after the first was dropped.
+  """
+  planner = PlanReActPlanner()
+  response_parts = [
+      types.Part.from_function_call(name="get_weather", args={"city": "SF"}),
+      types.Part.from_function_call(name="get_time", args={"city": "SF"}),
+  ]
+
+  result = planner.process_planning_response(
+      callback_context=None, response_parts=response_parts
+  )
+
+  assert _function_call_names(result) == ["get_weather", "get_time"]
+
+
+def test_preserves_parallel_function_calls_after_leading_text():
+  """The same parallel group is preserved when text comes first."""
+  planner = PlanReActPlanner()
+  response_parts = [
+      types.Part(text="Let me look that up."),
+      types.Part.from_function_call(name="get_weather", args={"city": "SF"}),
+      types.Part.from_function_call(name="get_time", args={"city": "SF"}),
+  ]
+
+  result = planner.process_planning_response(
+      callback_context=None, response_parts=response_parts
+  )
+
+  assert _function_call_names(result) == ["get_weather", "get_time"]