diff --git a/index.c b/index.c
index 8495ebd..4d9a333 100644
--- a/index.c
+++ b/index.c
@@ -292,7 +292,10 @@ static void *worker_pipeline(void *shared, int step, void *in)
         step_t *s = (step_t*)in;
 		for (i = 0; i < s->n_seq; ++i) {
 			mm_bseq1_t *t = &s->seq[i];
-			mm_sketch(0, t->seq, t->l_seq, p->mi->w, p->mi->k, t->rid, p->mi->flag&MM_I_HPC, &s->a);
+			if (t->l_seq > 0)
+				mm_sketch(0, t->seq, t->l_seq, p->mi->w, p->mi->k, t->rid, p->mi->flag&MM_I_HPC, &s->a);
+			else if (mm_verbose >= 2)
+				fprintf(stderr, "[WARNING] the length database sequence '%s' is 0\n", t->name);
 			free(t->seq); free(t->name);
 		}
 		free(s->seq); s->seq = 0;
diff --git a/main.c b/main.c
index 833edbe..cbd9f73 100644
--- a/main.c
+++ b/main.c
@@ -6,7 +6,7 @@
 #include "mmpriv.h"
 #include "getopt.h"
 
-#define MM_VERSION "2.5-r609-dirty"
+#define MM_VERSION "2.5-r610-dirty"
 
 #ifdef __linux__
 #include <sys/resource.h>