diff --git a/engine/src/flutter/lib/ui/painting.dart b/engine/src/flutter/lib/ui/painting.dart
index 3783920590b..8be94261688 100644
--- a/engine/src/flutter/lib/ui/painting.dart
+++ b/engine/src/flutter/lib/ui/painting.dart
@@ -2895,6 +2895,10 @@ class PathMetric {
       contourIndex = _measure.currentContourIndex;
 
   /// Return the total length of the current contour.
+  ///
+  /// The length may be calculated from an approximation of the geometry
+  /// originally added. For this reason, it is not recommended to rely on
+  /// this property for mathematically correct lengths of common shapes.
   final double length;
 
   /// Whether the contour is closed.