diff --git a/passphrase_cache.cc b/passphrase_cache.cc
index 57c0f35..c4211d4 100644
--- a/passphrase_cache.cc
+++ b/passphrase_cache.cc
@@ -24,6 +24,8 @@ namespace pEp {
     {
         while (!_cache.empty() && _cache.front().tp < clock::now() - _timeout)
             _cache.pop_front();
+        while (_cache.size() > _max_size)
+            _cache.pop_front();
     }
 };
 
diff --git a/passphrase_cache.hh b/passphrase_cache.hh
index d74e3be..83ca0eb 100644
--- a/passphrase_cache.hh
+++ b/passphrase_cache.hh
@@ -19,11 +19,12 @@ namespace pEp {
 
         std::list<cache_entry> _cache;   
         std::mutex _mtx;
+        int _max_size;
         duration _timeout;
 
     public:
-        PassphraseCache(duration timeout = std::chrono::minutes(10)) :
-            _timeout(timeout) { }
+        PassphraseCache(int max_size=20, duration timeout = std::chrono::minutes(10)) :
+            _max_size(max_size), _timeout(timeout) { }
         ~PassphraseCache() { }
         PassphraseCache(const PassphraseCache& second) :
             _cache(second._cache), _timeout(second._timeout) { }
diff --git a/test/test_passphrase_cache.cc b/test/test_passphrase_cache.cc
index 77c5f43..29ed967 100644
--- a/test/test_passphrase_cache.cc
+++ b/test/test_passphrase_cache.cc
@@ -6,7 +6,8 @@
 
 int main()
 {
-    pEp::PassphraseCache cache{std::chrono::seconds(1)};
+    pEp::PassphraseCache cache{2, std::chrono::seconds(1)};
+    cache.add("say");
     cache.add("hello");
     cache.add("world");