diff --git a/pkgs/source_span/CHANGELOG.md b/pkgs/source_span/CHANGELOG.md
index d1bcda5..6da8487 100644
--- a/pkgs/source_span/CHANGELOG.md
+++ b/pkgs/source_span/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 1.2.4
+
+* Fix a new strong mode error.
+
 # 1.2.3
 
 * Fix a bug where a point span at the end of a file without a trailing newline
diff --git a/pkgs/source_span/lib/src/span_mixin.dart b/pkgs/source_span/lib/src/span_mixin.dart
index f6d04fa..a258cf5 100644
--- a/pkgs/source_span/lib/src/span_mixin.dart
+++ b/pkgs/source_span/lib/src/span_mixin.dart
@@ -60,7 +60,7 @@
     if (length == 0 && this is! SourceSpanWithContext) return buffer.toString();
     buffer.write("\n");
 
-    var textLine;
+    String textLine;
     if (this is SourceSpanWithContext) {
       var context = (this as SourceSpanWithContext).context;
       var lineStart = findLineStart(context, text, column);
diff --git a/pkgs/source_span/pubspec.yaml b/pkgs/source_span/pubspec.yaml
index 3ef97ed..9e41fdd 100644
--- a/pkgs/source_span/pubspec.yaml
+++ b/pkgs/source_span/pubspec.yaml
@@ -1,5 +1,5 @@
 name: source_span
-version: 1.2.3
+version: 1.2.4
 author: Dart Team <misc@dartlang.org>
 description: A library for identifying source spans and locations.
 homepage: https://github.com/dart-lang/source_span