diff --git a/include/olm/olm.h b/include/olm/olm.h
index e5aff67..e35ed0a 100644
--- a/include/olm/olm.h
+++ b/include/olm/olm.h
@@ -307,7 +307,7 @@ size_t olm_create_outbound_session_random_length(
  * be "NOT_ENOUGH_RANDOM". */
 size_t olm_create_outbound_session(
     OlmSession * session,
-    OlmAccount * account,
+    OlmAccount const * account,
     void const * their_identity_key, size_t their_identity_key_length,
     void const * their_one_time_key, size_t their_one_time_key_length,
     void * random, size_t random_length
diff --git a/src/olm.cpp b/src/olm.cpp
index 660b21b..6dfa876 100644
--- a/src/olm.cpp
+++ b/src/olm.cpp
@@ -504,7 +504,7 @@ size_t olm_create_outbound_session_random_length(
 
 size_t olm_create_outbound_session(
     OlmSession * session,
-    OlmAccount * account,
+    OlmAccount const * account,
     void const * their_identity_key, size_t their_identity_key_length,
     void const * their_one_time_key, size_t their_one_time_key_length,
     void * random, size_t random_length