diff --git a/libgfortran/ChangeLog b/libgfortran/ChangeLog
index 8600a36997d..33976de7627 100644
--- a/libgfortran/ChangeLog
+++ b/libgfortran/ChangeLog
@@ -1,3 +1,10 @@
+2017-12-29  Jerry DeLisle  <jvdelisle@gcc.gnu.org>
+
+	Backport from trunk
+	PR libgfortran/83613
+	* io/unit.c (init_units): Don't forget to unlock the unit locks
+	after being inserted.
+
 2017-12-16  Jerry DeLisle  <jvdelisle@gcc.gnu.org>
 
 	Backport from trunk
diff --git a/libgfortran/io/unit.c b/libgfortran/io/unit.c
index 769c7cc1da2..c81d89ca716 100644
--- a/libgfortran/io/unit.c
+++ b/libgfortran/io/unit.c
@@ -689,7 +689,9 @@ init_units (void)
     }
   /* The default internal units.  */
   u = insert_unit (GFC_INTERNAL_UNIT);
+  __gthread_mutex_unlock (&u->lock);
   u = insert_unit (GFC_INTERNAL_UNIT4);
+  __gthread_mutex_unlock (&u->lock);
 
   /* Calculate the maximum file offset in a portable manner.
      max will be the largest signed number for the type gfc_offset.