diff --git a/indra/llcommon/aisyncclient.cpp b/indra/llcommon/aisyncclient.cpp
index 926197338..191a2627d 100644
--- a/indra/llcommon/aisyncclient.cpp
+++ b/indra/llcommon/aisyncclient.cpp
@@ -90,7 +90,7 @@
 bool operator==(AISyncKey const& key1, AISyncKey const& key2)
 {
   // Test if these keys match based on time.
-  if (std::abs((key1.mStartFrameCount - key2.mStartFrameCount)) > 1 &&
+  if (std::abs((S64)(key1.mStartFrameCount - key2.mStartFrameCount)) > 1 &&
 	  std::abs(key1.mFrameTimer.getStartTime() - key2.mFrameTimer.getStartTime()) >= sSyncKeyExpirationTime)
   {
 	return false;