--- a/dom/grid/GridLines.cpp
+++ b/dom/grid/GridLines.cpp
@@ -140,16 +140,24 @@ GridLines::SetLineInfo(const ComputedGri
       const nsTArray<nsString>& possiblyDuplicateLineNames(
         aLineInfo->mNames.SafeElementAt(i, nsTArray<nsString>()));
 
       nsTArray<nsString> lineNames;
       AddLineNamesIfNotPresent(lineNames, possiblyDuplicateLineNames);
 
       // Add in names from grid areas where this line is used as a boundary.
       for (auto area : aAreas) {
+        // We specifically ignore line names from implicitly named areas,
+        // because it can be confusing for designers who might naturally use
+        // a named line of "-start" or "-end" and create an implicit named
+        // area without meaning to.
+        if (area->Type() == GridDeclaration::Implicit) {
+          continue;
+        }
+
         bool haveNameToAdd = false;
         nsAutoString nameToAdd;
         area->GetName(nameToAdd);
         if (aIsRow) {
           if (area->RowStart() == line1Index) {
             haveNameToAdd = true;
             nameToAdd.AppendLiteral("-start");
           } else if (area->RowEnd() == line1Index) {