diff --git a/library/lms.c b/library/lms.c
index 78886ab..11e2508 100644
--- a/library/lms.c
+++ b/library/lms.c
@@ -101,6 +101,9 @@
     size_t output_hash_len;
     unsigned char r_node_idx_bytes[4];
 
+    /* Always zeroize the output buffer to avoid undefined behavior at an early exit */
+    memset(out, 0, MBEDTLS_LMS_M_NODE_BYTES(params->type));
+
     op = psa_hash_operation_init();
     status = psa_hash_setup(&op, PSA_ALG_SHA_256);
     if (status != PSA_SUCCESS) {