diff --git a/format.c b/format.c
index 0dd943a..890335c 100644
--- a/format.c
+++ b/format.c
@@ -274,7 +274,7 @@ double mm_event_identity(const mm_reg1_t *r)
 		if (op == 1 || op == 2)
 			++n_gapo, n_gap += len;
 	}
-	return (double)r->mlen / (r->blen - n_gap + n_gapo);
+	return (double)r->mlen / (r->blen + r->p->n_ambi - n_gap + n_gapo);
 }
 
 static inline void write_tags(kstring_t *s, const mm_reg1_t *r)
diff --git a/main.c b/main.c
index 35ebdf2..17dacc6 100644
--- a/main.c
+++ b/main.c
@@ -7,7 +7,7 @@
 #include "mmpriv.h"
 #include "ketopt.h"
 
-#define MM_VERSION "2.17-r968-dirty"
+#define MM_VERSION "2.17-r972-dirty"
 
 #ifdef __linux__
 #include <sys/resource.h>