1 files changed, 4 insertions, 2 deletions
diff --git a/RingBuffer.hs b/RingBuffer.hs
index b2779d7..64b0624 100644
--- a/RingBuffer.hs
+++ b/RingBuffer.hs
@@ -66,5 +66,7 @@ pushBack r upd = do
 updateBack :: RingBuffer u -> u -> IO ()
 updateBack r upd = do
-    back <- readIORef $ rBack r
+    size <- readIORef $ rSize r
-    updateBuffer (rBuffer r) back upd
+    when (size > 0) $ do
+        back <- readIORef $ rBack r
+        updateBuffer (rBuffer r) (mod (back + ringCapacity r - 1) (ringCapacity r)) upd

diff --git a/RingBuffer.hs b/RingBuffer.hs index b2779d7..64b0624 100644 --- a/RingBuffer.hs +++ b/RingBuffer.hs
@@ -66,5 +66,7 @@ pushBack r upd = do
66		66
67	updateBack :: RingBuffer u -> u -> IO ()	67	updateBack :: RingBuffer u -> u -> IO ()
68	updateBack r upd = do	68	updateBack r upd = do
69	back <- readIORef $ rBack r	69	size <- readIORef $ rSize r
70	updateBuffer (rBuffer r) back upd	70	when (size > 0) $ do
		71	back <- readIORef $ rBack r
		72	updateBuffer (rBuffer r) (mod (back + ringCapacity r - 1) (ringCapacity r)) upd