1 files changed, 2 insertions, 1 deletions
diff --git a/haskell/Data/VCDIFF/XDelta.hsc b/haskell/Data/VCDIFF/XDelta.hsc
index b406c1d..c66dab2 100644
--- a/haskell/Data/VCDIFF/XDelta.hsc
+++ b/haskell/Data/VCDIFF/XDelta.hsc
@@ -75,7 +75,8 @@ sourceWriteCurrentBlock :: PrimMonad m => Source m -> CurrentBlock -> m ()
 sourceWriteCurrentBlock (Source src) (CurrentBlock no sz ptr) = do
    writeAtByte src (#{off xd3_source, curblkno}) no
    writeAtByte src (#{off xd3_source, onblk})    sz
-    writeAtByte src (#{off xd3_source, curblk})   ptr
+    when (ptr /= nullPtr)
+        $ writeAtByte src (#{off xd3_source, curblk})   ptr
 sourceWriteEOFKnown :: PrimMonad m => Source m -> Bool -> m ()
 sourceWriteEOFKnown (Source src) False = writeAtByte src (#{off xd3_source, eof_known}) (0 :: #{type int})

diff --git a/haskell/Data/VCDIFF/XDelta.hsc b/haskell/Data/VCDIFF/XDelta.hsc index b406c1d..c66dab2 100644 --- a/haskell/Data/VCDIFF/XDelta.hsc +++ b/haskell/Data/VCDIFF/XDelta.hsc
@@ -75,7 +75,8 @@ sourceWriteCurrentBlock :: PrimMonad m => Source m -> CurrentBlock -> m ()
75	sourceWriteCurrentBlock (Source src) (CurrentBlock no sz ptr) = do	75	sourceWriteCurrentBlock (Source src) (CurrentBlock no sz ptr) = do
76	writeAtByte src (#{off xd3_source, curblkno}) no	76	writeAtByte src (#{off xd3_source, curblkno}) no
77	writeAtByte src (#{off xd3_source, onblk}) sz	77	writeAtByte src (#{off xd3_source, onblk}) sz
78	writeAtByte src (#{off xd3_source, curblk}) ptr	78	when (ptr /= nullPtr)
		79	$ writeAtByte src (#{off xd3_source, curblk}) ptr
79		80
80	sourceWriteEOFKnown :: PrimMonad m => Source m -> Bool -> m ()	81	sourceWriteEOFKnown :: PrimMonad m => Source m -> Bool -> m ()
81	sourceWriteEOFKnown (Source src) False = writeAtByte src (#{off xd3_source, eof_known}) (0 :: #{type int})	82	sourceWriteEOFKnown (Source src) False = writeAtByte src (#{off xd3_source, eof_known}) (0 :: #{type int})