--- a/layout/base/nsBidi.cpp
+++ b/layout/base/nsBidi.cpp
@@ -1479,32 +1479,33 @@ void nsBidi::ResolveImplicitLevels(int32
 {
   const DirProp *dirProps = mDirProps;
   DirProp dirProp;
   LevState levState;
   int32_t i, start1, start2;
   uint16_t oldStateImp, stateImp, actionImp;
   uint8_t gprop, resProp, cell;
 
+  memset(&levState, 0, sizeof(LevState));
   /* initialize for property and levels state tables */
   levState.runStart = aStart;
   levState.runLevel = mLevels[aStart];
   levState.pImpTab = impTab[levState.runLevel & 1];
   levState.pImpAct = impAct0;
 
   /* The isolates[] entries contain enough information to
      resume the bidi algorithm in the same state as it was
      when it was interrupted by an isolate sequence. */
   if (dirProps[aStart] == PDI && mIsolateCount >= 0) {
     start1 = mIsolates[mIsolateCount].start1;
     stateImp = mIsolates[mIsolateCount].stateImp;
     levState.state = mIsolates[mIsolateCount].state;
     mIsolateCount--;
   } else {
-    levState.startON = -1;
+    levState.startON = 0;
     start1 = aStart;
     if (dirProps[aStart] == NSM) {
       stateImp = 1 + aSOR;
     } else {
       stateImp = 0;
     }
     levState.state = 0;
     ProcessPropertySeq(&levState, aSOR, aStart, aStart);