diff --git a/docs/utilities/spacing.md b/docs/utilities/spacing.md
index 045c4b2139a759342e277e6f057db2a398808ded..da89ecfa0e3f2e5cc99ed7d936719fb3cc39f6ef 100644
--- a/docs/utilities/spacing.md
+++ b/docs/utilities/spacing.md
@@ -29,6 +29,7 @@ Where *size* is one of:
 * `1` - (by default) for classes that set the `margin` or `padding` to `$spacer-x` or `$spacer-y`
 * `2` - (by default) for classes that set the `margin` or `padding` to `$spacer-x * 1.5` or `$spacer-y * 1.5`
 * `3` - (by default) for classes that set the `margin` or `padding` to `$spacer-x * 3` or `$spacer-y * 3`
+* `auto` - for classes that set the `margin` to `auto`
 
 (You can add more sizes by adding entries to the `$spacers` Sass map variable.)
 
@@ -53,8 +54,7 @@ Here are some representative examples of these classes:
 }
 {% endhighlight %}
 
-### Horizontal centering
-Additionally, Bootstrap also includes an `.m-x-auto` class for horizontally centering fixed-width block level content by setting the horizontal margins to `auto`.
+The `.m-x-auto` class can be used for horizontally centering fixed-width block level content by setting the horizontal margins to `auto`.
 
 <div class="bd-example">
   <div class="m-x-auto" style="width: 200px; background-color: rgba(86,61,124,.15);">
diff --git a/scss/_variables.scss b/scss/_variables.scss
index 86a29e23c3355f7efab30ef37afcd933de5b4bee..897ef9d030c9600d3a14f92bd469230466609788 100644
--- a/scss/_variables.scss
+++ b/scss/_variables.scss
@@ -95,6 +95,10 @@ $spacers: (
   3: (
     x: ($spacer-x * 3),
     y: ($spacer-y * 3)
+  ),
+  auto: (
+    x: auto,
+    y: auto
   )
 ) !default;
 $border-width: 1px !default;
diff --git a/scss/utilities/_spacing.scss b/scss/utilities/_spacing.scss
index b7ff044b6dba2dd2e9534f1a074800dbbdb677f2..8bb2d44d5b17f13ef2c7e1c13ef2dfab60755589 100644
--- a/scss/utilities/_spacing.scss
+++ b/scss/utilities/_spacing.scss
@@ -4,11 +4,6 @@
 
 // Margin and Padding
 
-.m-x-auto {
-  margin-right: auto !important;
-  margin-left:  auto !important;
-}
-
 @each $prop, $abbrev in (margin: m, padding: p) {
   @each $size, $lengths in $spacers {
     $length-x:   map-get($lengths, x);