diff --git a/lib/regexec.c b/lib/regexec.c
index 5e4eb497a..f25e00d83 100644
--- a/lib/regexec.c
+++ b/lib/regexec.c
@@ -1674,6 +1674,8 @@ build_sifted_states (const re_match_context_t *mctx, re_sift_context_t *sctx,
 static reg_errcode_t
 clean_state_log_if_needed (re_match_context_t *mctx, Idx next_state_log_idx)
 {
+  DEBUG_ASSERT (mctx->state_log != NULL);
+
   Idx top = mctx->state_log_top;
 
   if ((next_state_log_idx >= mctx->input.bufs_len