diff --git a/libgfortran/ChangeLog b/libgfortran/ChangeLog
index 4e9c5c7c7a46..dbfc5d353424 100644
--- a/libgfortran/ChangeLog
+++ b/libgfortran/ChangeLog
@@ -1,3 +1,8 @@
+2018-06-09  Jerry DeLisle  <jvdelisle@gcc.gnu.org>
+
+	PR libgfortran/86070
+	* io/write_float.def (build_float_string): Initialize *len.
+
 2018-06-01  Steven G. Kargl  <kargl@gcc.gnu.org>
 
 	PR fortran/85816
diff --git a/libgfortran/io/write_float.def b/libgfortran/io/write_float.def
index 177a568e041d..25ea64beb212 100644
--- a/libgfortran/io/write_float.def
+++ b/libgfortran/io/write_float.def
@@ -135,6 +135,7 @@ build_float_string (st_parameter_dt *dtp, const fnode *f, char *buffer,
   w = f->u.real.w;
   d = f->u.real.d;
   p = dtp->u.p.scale_factor;
+  *len = 0;
 
   rchar = '5';