flatten.patch

diff --git a/base/iterators.jl b/base/iterators.jl
index 1c2ab13..4e5d1b5 100644
--- a/base/iterators.jl
+++ b/base/iterators.jl
@@ -694,28 +694,30 @@ function start(f::Flatten)
     d = done(f.it, s)
     # this is a simple way to make this function type stable
     d && throw(ArgumentError("argument to Flatten must contain at least one iterator"))
+    done_inner = false
     while !d
         inner, s = next(f.it, s)
         s2 = start(inner)
-        !done(inner, s2) && break
+        done_inner = done(inner, s2)
+        !done_inner && break
         d = done(f.it, s)
     end
-    return s, inner, s2
+    return (d & done_inner), s, inner, s2
 end
 
 @inline function next(f::Flatten, state)
-    s, inner, s2 = state
+    _done, s, inner, s2 = state
     val, s2 = next(inner, s2)
-    while done(inner, s2) && !done(f.it, s)
+    done_inner = done_outer = false
+    while (done_inner=done(inner, s2)) && !(done_outer=done(f.it, s))
         inner, s = next(f.it, s)
         s2 = start(inner)
     end
-    return val, (s, inner, s2)
+    return val, ((done_inner & done_outer), s, inner, s2)
 end
 
 @inline function done(f::Flatten, state)
-    s, inner, s2 = state
-    return done(f.it, s) && done(inner, s2)
+    return state[1]
 end