diff --git a/src/govuk/settings/_measurements.scss b/src/govuk/settings/_measurements.scss
index 027548cb3b..7f103b94d5 100644
--- a/src/govuk/settings/_measurements.scss
+++ b/src/govuk/settings/_measurements.scss
@@ -81,6 +81,9 @@ $govuk-border-width-form-element: 2px !default;
 ///
 /// @type Number
 /// @access public
+/// @deprecated Use $govuk-border-width-form-element instead. There should be no
+///   difference in thickness for inputs in the error state, in order to
+///   maintain a distinct focus state.
 
 $govuk-border-width-form-element-error: 2px !default;