diff --git a/pkgs/source_span/lib/src/highlighter.dart b/pkgs/source_span/lib/src/highlighter.dart
index d61ff9f..1c39185 100644
--- a/pkgs/source_span/lib/src/highlighter.dart
+++ b/pkgs/source_span/lib/src/highlighter.dart
@@ -292,7 +292,9 @@
             ? _primaryColor
             : _secondaryColor;
     var foundCurrent = false;
-    for (var highlight in highlightsByColumn) {
+    for (var tmp in highlightsByColumn) {
+      // Work around https://github.com/dart-lang/sdk/issues/43136
+      final highlight = tmp;
       final startLine = highlight?.span.start.line;
       final endLine = highlight?.span.end.line;
       if (current != null && highlight == current) {
@@ -326,9 +328,9 @@
             }, color: openedOnThisLineColor);
             openedOnThisLine = true;
             openedOnThisLineColor ??=
-                highlight!.isPrimary ? _primaryColor : _secondaryColor;
+                highlight.isPrimary ? _primaryColor : _secondaryColor;
           } else if (endLine == line.number &&
-              highlight!.span.end.column == line.text.length) {
+              highlight.span.end.column == line.text.length) {
             _buffer.write(highlight.label == null
                 ? glyph.glyphOrAscii('└', '\\')
                 : vertical);