diff --git a/src/gutter-component.coffee b/src/gutter-component.coffee
index fa04c0afc..22d9b224a 100644
--- a/src/gutter-component.coffee
+++ b/src/gutter-component.coffee
@@ -120,7 +120,7 @@ GutterComponent = React.createClass
     node = @refs.lineNumbers.getDOMNode()
     for lineNumberId, lineNumberNode of @lineNumberNodesById when not lineNumberIdsToPreserve?.has(lineNumberId)
       screenRow = @screenRowsByLineNumberId[lineNumberId]
-      unless screenRow is mouseWheelScreenRow
+      if not screenRow? or screenRow isnt mouseWheelScreenRow
         delete @lineNumberNodesById[lineNumberId]
         delete @lineNumberIdsByScreenRow[screenRow] if @lineNumberIdsByScreenRow[screenRow] is lineNumberId
         delete @screenRowsByLineNumberId[lineNumberId]
diff --git a/src/lines-component.coffee b/src/lines-component.coffee
index b70f33820..4e2741214 100644
--- a/src/lines-component.coffee
+++ b/src/lines-component.coffee
@@ -79,7 +79,7 @@ LinesComponent = React.createClass
     node = @getDOMNode()
     for lineId, lineNode of @lineNodesByLineId when not visibleLineIds.has(lineId)
       screenRow = @screenRowsByLineId[lineId]
-      unless screenRow is mouseWheelScreenRow
+      if not screenRow? or screenRow isnt mouseWheelScreenRow
         delete @lineNodesByLineId[lineId]
         delete @lineIdsByScreenRow[screenRow] if @lineIdsByScreenRow[screenRow] is lineId
         delete @screenRowsByLineId[lineId]