diff --git a/format.c b/format.c
index 115c362..048ca3e 100644
--- a/format.c
+++ b/format.c
@@ -145,4 +145,5 @@ void mm_write_sam(kstring_t *s, const mm_idx_t *mi, const bseq1_t *t, const mm_r
 		}
 		write_tags(s, r);
 	}
+	s->s[s->l] = 0; // we always have room for an extra byte (see str_enlarge)
 }
diff --git a/main.c b/main.c
index 39a32c9..68b9691 100644
--- a/main.c
+++ b/main.c
@@ -10,7 +10,7 @@
 #include "minimap.h"
 #include "mmpriv.h"
 
-#define MM_VERSION "2.0-r180-dirty"
+#define MM_VERSION "2.0-r187-dirty"
 
 void liftrlimit()
 {