diff --git a/fdbserver/storageserver.actor.cpp b/fdbserver/storageserver.actor.cpp
index c8e7118fef..336381761a 100644
--- a/fdbserver/storageserver.actor.cpp
+++ b/fdbserver/storageserver.actor.cpp
@@ -1011,6 +1011,11 @@ ACTOR Future<Void> getValueQ( StorageServer* data, GetValueRequest req ) {
 	return Void();
 };
 
+// Pessimistic estimate the number of overhead bytes used by each
+// watch. Watch key references are stored in an AsyncMap<Key,bool>, and actors
+// must be kept alive until the watch is finished.
+static constexpr size_t WATCH_OVERHEAD_BYTES = 1000;
+
 ACTOR Future<Void> watchValue_impl( StorageServer* data, WatchValueRequest req ) {
 	try {
 		++data->counters.watchQueries;
@@ -1058,7 +1063,7 @@ ACTOR Future<Void> watchValue_impl( StorageServer* data, WatchValueRequest req )
 				}
 
 				++data->numWatches;
-				data->watchBytes += ( req.key.expectedSize() + req.value.expectedSize() + 1000 );
+				data->watchBytes += (req.key.expectedSize() + req.value.expectedSize() + WATCH_OVERHEAD_BYTES);
 				try {
 					if(latest < minVersion) {
 						// If the version we read is less than minVersion, then we may fail to be notified of any changes that occur up to or including minVersion
@@ -1071,10 +1076,10 @@ ACTOR Future<Void> watchValue_impl( StorageServer* data, WatchValueRequest req )
 					}
 					wait(watchFuture);
 					--data->numWatches;
-					data->watchBytes -= ( req.key.expectedSize() + req.value.expectedSize() + 1000 );
+					data->watchBytes -= (req.key.expectedSize() + req.value.expectedSize() + WATCH_OVERHEAD_BYTES);
 				} catch( Error &e ) {
 					--data->numWatches;
-					data->watchBytes -= ( req.key.expectedSize() + req.value.expectedSize() + 1000 );
+					data->watchBytes -= (req.key.expectedSize() + req.value.expectedSize() + WATCH_OVERHEAD_BYTES);
 					throw;
 				}
 			} catch( Error &e ) {