diff --git a/tests/test_group_session.cpp b/tests/test_group_session.cpp
index 251971c..59b0a20 100644
--- a/tests/test_group_session.cpp
+++ b/tests/test_group_session.cpp
@@ -55,7 +55,7 @@ int main() {
     /* Deliberately corrupt the pickled session by supplying a junk suffix and
     * ensure this is caught as an error. */
     const size_t junk_length = 1;
-    std::vector<std::uint8_t> junk_pickle(pickle_length + junk_length);
+    std::vector<std::uint8_t> junk_pickle(pickle_length + _olm_enc_output_length(junk_length));
 
     olm_pickle_outbound_group_session(
         session, "secret_key", 10, junk_pickle.data(), pickle_length
@@ -110,7 +110,7 @@ int main() {
     /* Deliberately corrupt the pickled session by supplying a junk suffix and
     * ensure this is caught as an error. */
     const size_t junk_length = 1;
-    std::vector<std::uint8_t> junk_pickle(pickle_length + junk_length);
+    std::vector<std::uint8_t> junk_pickle(pickle_length + _olm_enc_output_length(junk_length));
 
     olm_pickle_inbound_group_session(
         session, "secret_key", 10, junk_pickle.data(), pickle_length
diff --git a/tests/test_olm.cpp b/tests/test_olm.cpp
index 215b180..d95be79 100644
--- a/tests/test_olm.cpp
+++ b/tests/test_olm.cpp
@@ -71,7 +71,7 @@ assert_equals(pickle1.data(), pickle2.data(), pickle_length);
 /* Deliberately corrupt the pickled account by supplying a junk suffix and
  * ensure this is caught as an error. */
 const size_t junk_length = 1;
-std::vector<std::uint8_t> junk_pickle(pickle_length + junk_length);
+std::vector<std::uint8_t> junk_pickle(pickle_length + _olm_enc_output_length(junk_length));
 
 res = ::olm_pickle_account(
     account, "secret_key", 10, junk_pickle.data(), pickle_length);
@@ -162,7 +162,7 @@ assert_equals(pickle1.data(), pickle2.data(), pickle_length);
 /* Deliberately corrupt the pickled session by supplying a junk suffix and
  * ensure this is caught as an error. */
 const size_t junk_length = 1;
-std::vector<std::uint8_t> junk_pickle(pickle_length + junk_length);
+std::vector<std::uint8_t> junk_pickle(pickle_length + _olm_enc_output_length(junk_length));
 
 res = ::olm_pickle_session(
     session, "secret_key", 10, junk_pickle.data(), pickle_length);
diff --git a/tests/test_pk.cpp b/tests/test_pk.cpp
index f975029..3b3cb48 100644
--- a/tests/test_pk.cpp
+++ b/tests/test_pk.cpp
@@ -146,7 +146,7 @@ assert_equals(alice_public, pubkey.data(), olm_pk_key_length());
  * ensure this is caught as an error. */
 const size_t junk_length = 1;
 std::size_t pickle_length = olm_pickle_pk_decryption_length(decryption);
-std::vector<std::uint8_t> junk_pickle(pickle_length + junk_length);
+std::vector<std::uint8_t> junk_pickle(pickle_length + _olm_enc_output_length(junk_length));
 
 olm_pickle_pk_decryption(
     decryption,