diff --git a/folio/graph.py b/folio/graph.py
index a88b165..c8a8d5a 100644
--- a/folio/graph.py
+++ b/folio/graph.py
@@ -21,7 +21,7 @@
 import time
 import traceback
 from enum import Enum
-from functools import cache
+from functools import cache, lru_cache
 from pathlib import Path
 from typing import Dict, List, Literal, Optional, Tuple
 
@@ -124,9 +124,21 @@ class FOLIOTypes(Enum):
 # minimum length for prefix search
 MIN_PREFIX_LENGTH: int = 3
 
+# Bound query-result caches so long-running processes cannot retain every unique search forever.
+DEFAULT_SEARCH_CACHE_SIZE: int = 128
+
 # Set up logger
 LOGGER = get_logger(__name__)
 
+
+def _store_prefix_cache(
+    cache_map: Dict[str, List[OWLClass]], key: str, classes: List[OWLClass]
+) -> None:
+    """Store one prefix-search result and evict the oldest entry at capacity."""
+    cache_map[key] = classes
+    while len(cache_map) > DEFAULT_SEARCH_CACHE_SIZE:
+        cache_map.pop(next(iter(cache_map)))
+
 # try to import rapidfuzz and marisa_trie with importlib; log if not able to.
 try:
     if importlib.util.find_spec("rapidfuzz") is not None:
@@ -1384,7 +1396,7 @@ def _search_by_prefix_sensitive(self, prefix: str) -> List[OWLClass]:
                     iri_list.append(idx)
 
         classes = [self[index] for index in iri_list]
-        self._prefix_cache[prefix] = classes  # type: ignore[assignment]
+        _store_prefix_cache(self._prefix_cache, prefix, classes)
         return classes
 
     def _search_by_prefix_insensitive(self, prefix: str) -> List[OWLClass]:
@@ -1436,11 +1448,11 @@ def _search_by_prefix_insensitive(self, prefix: str) -> List[OWLClass]:
                     iri_list.append(idx)
 
         classes = [self[index] for index in iri_list]
-        self._ci_prefix_cache[folded] = classes  # type: ignore[assignment]
+        _store_prefix_cache(self._ci_prefix_cache, folded, classes)
         return classes
 
     @staticmethod
-    @cache
+    @lru_cache(maxsize=DEFAULT_SEARCH_CACHE_SIZE)
     def _basic_search(
         query: str,
         search_list: Tuple[str],
diff --git a/tests/test_folio.py b/tests/test_folio.py
index f62d83e..0763916 100644
--- a/tests/test_folio.py
+++ b/tests/test_folio.py
@@ -345,6 +345,30 @@ def test_search_prefix_fallback_parity(folio_graph, monkeypatch):
     )
 
 
+def test_search_caches_are_bounded(folio_graph):
+    """Unique search queries must not grow process-lifetime caches without bound."""
+    FOLIO._basic_search.cache_clear()
+    folio_graph._prefix_cache = {}
+    folio_graph._ci_prefix_cache = {}
+
+    try:
+        for index in range(129):
+            query = f"no-match-{index}"
+            FOLIO._basic_search(query, ("alpha", "beta"), limit=1)
+            folio_graph.search_by_prefix(query, case_sensitive=True)
+            folio_graph.search_by_prefix(query)
+
+        cache_info = FOLIO._basic_search.cache_info()
+        assert cache_info.maxsize == 128
+        assert cache_info.currsize == 128
+        assert len(folio_graph._prefix_cache) == 128
+        assert len(folio_graph._ci_prefix_cache) == 128
+    finally:
+        FOLIO._basic_search.cache_clear()
+        folio_graph._prefix_cache = {}
+        folio_graph._ci_prefix_cache = {}
+
+
 def test_search_label(folio_graph):
     for c, score in folio_graph.search_by_label("Georgia"):
         assert "Georgia" in c.label