diff --git a/litellm/litellm_core_utils/openai_tool_name_mapping.py b/litellm/litellm_core_utils/openai_tool_name_mapping.py
index 2994db371ac..dfce305ce87 100644
--- a/litellm/litellm_core_utils/openai_tool_name_mapping.py
+++ b/litellm/litellm_core_utils/openai_tool_name_mapping.py
@@ -1,13 +1,17 @@
 """
-Per-request mapping from OpenAI-safe tool names back to client-supplied names.
+Per-request mapping between client-supplied tool names and their OpenAI-safe forms.
 
 OpenAI's Chat Completions API requires tools[].function.name to match
 ``^[a-zA-Z0-9_-]+$``. For providers that enforce this, we rewrite outbound tool
-names and keep sanitized -> original in a ContextVar dict for this completion only
-(never a process-wide cache).
+names and keep two ContextVar dicts for this completion only (never a process-wide
+cache):
 
-Restore in ``convert_dict_to_response`` only affects names present in the current
-request's mapping, so other providers and concurrent requests are unaffected.
+  _CTX      – sanitized  → original   (used on the response path)
+  _CTX_REV  – original   → sanitized  (used to rewrite tool_choice before the request)
+
+Using the pre-built reverse map for tool_choice guarantees that collision suffixes
+(e.g. "a_b_1") added by _make_unique_openai_tool_name are respected instead of
+being recomputed independently.
 """
 
 from __future__ import annotations
@@ -18,6 +22,9 @@ from typing import Dict, Optional
 _CTX: contextvars.ContextVar[Optional[Dict[str, str]]] = contextvars.ContextVar(
     "litellm_openai_tool_name_mapping", default=None
 )
+_CTX_REV: contextvars.ContextVar[Optional[Dict[str, str]]] = contextvars.ContextVar(
+    "litellm_openai_tool_name_mapping_rev", default=None
+)
 
 # Providers where the upstream Chat Completions API applies OpenAI tool-name validation.
 _OPENAI_TOOL_NAME_VALIDATION_PROVIDERS = frozenset(
@@ -44,8 +51,9 @@ def should_sanitize_openai_tool_names(litellm_provider: str) -> bool:
 
 
 def begin_openai_tool_name_mapping_scope() -> None:
-    """Reset mapping for this completion (call once at the start of completion())."""
+    """Reset both mappings for this completion (call once at the start of completion())."""
     _CTX.set({})
+    _CTX_REV.set({})
 
 
 def _store(sanitized: str, original: str) -> None:
@@ -56,6 +64,11 @@ def _store(sanitized: str, original: str) -> None:
         m = {}
         _CTX.set(m)
     m[sanitized] = original
+    r = _CTX_REV.get()
+    if r is None:
+        r = {}
+        _CTX_REV.set(r)
+    r[original] = sanitized
 
 
 def get_openai_tool_name(response_tool_name: str) -> str:
@@ -74,3 +87,16 @@ def restore_openai_tool_name_for_user(sanitized_name: Optional[str]) -> Optional
 def store_openai_tool_name_mapping(sanitized: str, original: str) -> None:
     """Record a rewrite when ``validate_and_fix_openai_tools`` sanitizes a name."""
     _store(sanitized, original)
+
+
+def get_sanitized_tool_name(original_name: str) -> str:
+    """Return the sanitized (outbound) name for *original_name* if it was rewritten.
+
+    Used to rewrite ``tool_choice.function.name`` after ``validate_and_fix_openai_tools``
+    has run, so that collision suffixes added by ``_make_unique_openai_tool_name`` are
+    respected rather than recomputed independently.
+    """
+    r = _CTX_REV.get()
+    if r is not None and original_name in r:
+        return r[original_name]
+    return original_name
diff --git a/litellm/main.py b/litellm/main.py
index d47b625f6b3..5d881bdfc8b 100644
--- a/litellm/main.py
+++ b/litellm/main.py
@@ -1189,9 +1189,11 @@ def completion(  # type: ignore # noqa: PLR0915
     ):
         _fn = tool_choice.get("function")
         if isinstance(_fn, dict) and isinstance(_fn.get("name"), str):
-            from litellm.utils import _sanitize_openai_function_tool_name as _san_name
+            from litellm.litellm_core_utils.openai_tool_name_mapping import (
+                get_sanitized_tool_name as _get_sanitized,
+            )
 
-            _sanitized_tc_name = _san_name(_fn["name"], -1)
+            _sanitized_tc_name = _get_sanitized(_fn["name"])
             if _sanitized_tc_name != _fn["name"]:
                 tool_choice = {
                     **tool_choice,
diff --git a/tests/test_litellm/test_utils.py b/tests/test_litellm/test_utils.py
index bfbc216e2da..601650c3836 100644
--- a/tests/test_litellm/test_utils.py
+++ b/tests/test_litellm/test_utils.py
@@ -4117,8 +4117,9 @@ def test_convert_to_model_response_restores_openai_tool_call_names_when_mapped()
 def test_tool_choice_function_name_sanitized_with_tools():
     from litellm.litellm_core_utils.openai_tool_name_mapping import (
         begin_openai_tool_name_mapping_scope,
+        get_sanitized_tool_name,
     )
-    from litellm.utils import _sanitize_openai_function_tool_name, validate_and_fix_openai_tools
+    from litellm.utils import validate_and_fix_openai_tools
 
     begin_openai_tool_name_mapping_scope()
     validate_and_fix_openai_tools(
@@ -4133,11 +4134,44 @@ def test_tool_choice_function_name_sanitized_with_tools():
         ],
         sanitize_openai_function_tool_names=True,
     )
-    # Simulate what main.py does for tool_choice
+    # main.py uses get_sanitized_tool_name (reverse map) — not a re-computation
     tool_choice = {"type": "function", "function": {"name": "my.tool"}}
     _fn = tool_choice["function"]
-    sanitized = _sanitize_openai_function_tool_name(_fn["name"], -1)
+    sanitized = get_sanitized_tool_name(_fn["name"])
     if sanitized != _fn["name"]:
         tool_choice = {**tool_choice, "function": {**_fn, "name": sanitized}}
 
     assert tool_choice["function"]["name"] == "my_tool"
+
+
+def test_tool_choice_function_name_uses_collision_suffix():
+    """tool_choice pointing at the second of two colliding names must use the '_1' suffix."""
+    from litellm.litellm_core_utils.openai_tool_name_mapping import (
+        begin_openai_tool_name_mapping_scope,
+        get_sanitized_tool_name,
+    )
+    from litellm.utils import validate_and_fix_openai_tools
+
+    begin_openai_tool_name_mapping_scope()
+    validate_and_fix_openai_tools(
+        tools=[
+            {
+                "type": "function",
+                "function": {
+                    "name": "a.b",
+                    "parameters": {"type": "object", "properties": {}},
+                },
+            },
+            {
+                "type": "function",
+                "function": {
+                    "name": "a/b",
+                    "parameters": {"type": "object", "properties": {}},
+                },
+            },
+        ],
+        sanitize_openai_function_tool_names=True,
+    )
+    # "a.b" → "a_b"; "a/b" also sanitizes to "a_b" but gets suffix → "a_b_1"
+    assert get_sanitized_tool_name("a.b") == "a_b"
+    assert get_sanitized_tool_name("a/b") == "a_b_1"