diff --git a/src/libcrypto.c b/src/libcrypto.c
index 9ef00cb7..eefc98dd 100644
--- a/src/libcrypto.c
+++ b/src/libcrypto.c
@@ -708,8 +708,12 @@ aes_ctr_encrypt(struct ssh_cipher_struct *cipher,
 }
 
 static void aes_ctr_cleanup(struct ssh_cipher_struct *cipher){
-    explicit_bzero(cipher->aes_key, sizeof(*cipher->aes_key));
-    SAFE_FREE(cipher->aes_key);
+    if (cipher != NULL) {
+        if (cipher->aes_key != NULL) {
+            explicit_bzero(cipher->aes_key, sizeof(*cipher->aes_key));
+        }
+        SAFE_FREE(cipher->aes_key);
+    }
 }
 
 #endif /* HAVE_OPENSSL_EVP_AES_CTR */