diff --git a/src/libsodium/crypto_kx/crypto_kx.c b/src/libsodium/crypto_kx/crypto_kx.c
index 67e2f00e..1d5ee6ef 100644
--- a/src/libsodium/crypto_kx/crypto_kx.c
+++ b/src/libsodium/crypto_kx/crypto_kx.c
@@ -88,6 +88,9 @@ crypto_kx_server_session_keys(unsigned char rx[crypto_kx_SESSIONKEYBYTES],
     if (tx == NULL) {
         tx = rx;
     }
+    if (rx == NULL) {
+        abort();
+    }
     if (crypto_scalarmult(q, server_sk, client_pk) != 0) {
         return -1;
     }