diff --git a/src/crf/src/crf1d_model.c b/src/crf/src/crf1d_model.c
index 426fd9e..fb7e8e7 100644
--- a/src/crf/src/crf1d_model.c
+++ b/src/crf/src/crf1d_model.c
@@ -496,6 +496,11 @@ int crf1dmw_put_labelref(crf1dmw_t* writer, int lid, const feature_refs_t* ref,
         return CRFSUITEERR_INTERNAL_LOGIC;
     }
 
+    /* Validate lid is within bounds */
+    if (lid < 0 || (uint32_t)lid >= href->num) {
+        return CRFSUITEERR_INTERNAL_LOGIC;
+    }
+
     /* Store the current offset to the offset array. */
     href->offsets[lid] = ftell(fp);