diff --git a/litellm/caching/in_memory_cache.py b/litellm/caching/in_memory_cache.py
index 64e8bb3aafc..88708efcf14 100644
--- a/litellm/caching/in_memory_cache.py
+++ b/litellm/caching/in_memory_cache.py
@@ -193,6 +193,8 @@ class InMemoryCache(BaseCache):
         """
         # get the value
         init_value: Final = self.get_cache(key=key) or set()
+        if not isinstance(init_value, set):
+            raise TypeError("Cached value is not a set")
         for val in value:
             init_value.add(val)
         self.set_cache(key, init_value, ttl=ttl)
@@ -234,6 +236,8 @@ class InMemoryCache(BaseCache):
         with self._increment_lock:
             # keep read-modify-write atomic
             init_value: Final = self.get_cache(key=key) or 0
+            if not isinstance(init_value, (int, float)):
+                raise TypeError("Cached value is not numeric")
             value = init_value + value
             self.set_cache(key, value, **kwargs)
             return value
diff --git a/tests/unit/caching/test_in_memory_cache.py b/tests/unit/caching/test_in_memory_cache.py
index 5df35a942e2..9ace9992ba9 100644
--- a/tests/unit/caching/test_in_memory_cache.py
+++ b/tests/unit/caching/test_in_memory_cache.py
@@ -86,6 +86,22 @@ def test_increment_cache_is_atomic_under_thread_concurrency():
     assert cache.get_cache("counter") == seed + thread_count
 
 
+@pytest.mark.parametrize("bad_value", [{"count": 1}, [1], _CachedBudget(spend=1.0, events=[1])])
+def test_increment_cache_rejects_non_numeric_cached_values(bad_value):
+    cache = InMemoryCache()
+    cache.set_cache("counter", bad_value)
+    with pytest.raises(TypeError, match="Cached value is not numeric"):
+        cache.increment_cache("counter", 1)
+
+
+@pytest.mark.asyncio
+async def test_async_set_cache_sadd_rejects_non_set_cached_value():
+    cache = InMemoryCache()
+    cache.set_cache("members", ["one"])
+    with pytest.raises(TypeError, match="Cached value is not a set"):
+        await cache.async_set_cache_sadd("members", ["two"], ttl=None)
+
+
 async def test_async_increment_delegates_to_locked_sync_path():
     cache = InMemoryCache()
     assert await cache.async_increment("counter", 2) == 2