diff --git a/src/glu/sgi/libnurbs/nurbtess/monoChain.cc b/src/glu/sgi/libnurbs/nurbtess/monoChain.cc
index 814bf32fae0..b17b9405c1a 100644
--- a/src/glu/sgi/libnurbs/nurbtess/monoChain.cc
+++ b/src/glu/sgi/libnurbs/nurbtess/monoChain.cc
@@ -127,6 +127,7 @@ monoChain::monoChain(directedLine* cHead, directedLine* cTail)
     current = chainTail;
 
   isKey = 0;
+  keyY = 0;
 }
 
 //insert a new line between prev and this