1 files changed, 6 insertions, 4 deletions

diff --git a/lib/pure/streams.nim b/lib/pure/streams.nim
index 67c80e592..e706f2016 100644
--- a/lib/pure/streams.nim
+++ b/lib/pure/streams.nim
@@ -224,10 +224,12 @@ proc ssReadData(s: Stream, buffer: pointer, bufLen: int): int =
 
 proc ssWriteData(s: Stream, buffer: pointer, bufLen: int) = 
   var s = StringStream(s)
-  if bufLen > 0: 
-    setLen(s.data, s.data.len + bufLen)
-    copyMem(addr(s.data[s.pos]), buffer, bufLen)
-    inc(s.pos, bufLen)
+  if bufLen <= 0:
+    return
+  if s.pos + bufLen > s.data.len:
+    setLen(s.data, s.pos + bufLen)
+  copyMem(addr(s.data[s.pos]), buffer, bufLen)
+  inc(s.pos, bufLen)
 
 proc ssClose(s: Stream) =
   var s = StringStream(s)