diff --git a/CHANGELOG.md b/CHANGELOG.md
index ddb4ff0..0dfe483 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+# 1.5.6
+
+* Fix padding around line numbers that are powers of 10 in
+  `FileSpan.highlight()`.
+
 # 1.5.5
 
 * Fix a bug where `FileSpan.highlight()` would crash for spans that covered a
diff --git a/lib/src/highlighter.dart b/lib/src/highlighter.dart
index 17a47bc..0714acd 100644
--- a/lib/src/highlighter.dart
+++ b/lib/src/highlighter.dart
@@ -181,7 +181,7 @@
         // In a purely mathematical world, floor(log10(n)) would give the number of
         // digits in n, but floating point errors render that unreliable in
         // practice.
-        _paddingBeforeSidebar = _span.end.line.toString().length + 1;
+        _paddingBeforeSidebar = (_span.end.line + 1).toString().length + 1;
 
   /// Returns the highlighted span text.
   ///
diff --git a/test/highlight_test.dart b/test/highlight_test.dart
index 5fdf622..521f748 100644
--- a/test/highlight_test.dart
+++ b/test/highlight_test.dart
@@ -530,4 +530,30 @@
 ${colors.BLUE}  '${colors.NONE}"""));
     });
   });
+
+  group("line numbers have appropriate padding", () {
+    test("with line number 9", () {
+      expect(
+          SourceFile.fromString("\n" * 8 + "foo bar baz\n")
+              .span(8, 11)
+              .highlight(),
+          equals("""
+  ,
+9 | foo bar baz
+  | ^^^
+  '"""));
+    });
+
+    test("with line number 10", () {
+      expect(
+          SourceFile.fromString("\n" * 9 + "foo bar baz\n")
+              .span(9, 12)
+              .highlight(),
+          equals("""
+   ,
+10 | foo bar baz
+   | ^^^
+   '"""));
+    });
+  });
 }