diff --git a/common/changes/office-ui-fabric-react/undo-button-classname_2018-02-24-03-17.json b/common/changes/office-ui-fabric-react/undo-button-classname_2018-02-24-03-17.json
new file mode 100644
index 00000000000000..fee3aae26603be
--- /dev/null
+++ b/common/changes/office-ui-fabric-react/undo-button-classname_2018-02-24-03-17.json
@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "office-ui-fabric-react",
+      "comment": "Button: reverting previous tweak to fix ComboBox dropdown selection styling.",
+      "type": "patch"
+    }
+  ],
+  "packageName": "office-ui-fabric-react",
+  "email": "dzearing@microsoft.com"
+}
\ No newline at end of file
diff --git a/packages/office-ui-fabric-react/src/components/Breadcrumb/__snapshots__/Breadcrumb.test.tsx.snap b/packages/office-ui-fabric-react/src/components/Breadcrumb/__snapshots__/Breadcrumb.test.tsx.snap
index 9ea260d7df8d62..b4f337bfab5ce1 100644
--- a/packages/office-ui-fabric-react/src/components/Breadcrumb/__snapshots__/Breadcrumb.test.tsx.snap
+++ b/packages/office-ui-fabric-react/src/components/Breadcrumb/__snapshots__/Breadcrumb.test.tsx.snap
@@ -182,8 +182,8 @@ exports[`Breadcrumb renders breadcumb correctly 2`] = `
               aria-pressed={undefined}
               className=
                   ms-Button
-                  ms-Button--icon
                   ms-Breadcrumb-overflowButton
+                  ms-Button--icon
                   {
                     -moz-osx-font-smoothing: grayscale;
                     -webkit-font-smoothing: antialiased;
diff --git a/packages/office-ui-fabric-react/src/components/Button/BaseButton.classNames.ts b/packages/office-ui-fabric-react/src/components/Button/BaseButton.classNames.ts
index 65da87a32c14c9..688e667d0ef61a 100644
--- a/packages/office-ui-fabric-react/src/components/Button/BaseButton.classNames.ts
+++ b/packages/office-ui-fabric-react/src/components/Button/BaseButton.classNames.ts
@@ -30,6 +30,7 @@ export const getBaseButtonClassNames = memoizeFunction((
     root: [
       'ms-Button',
       styles.root,
+      className,
       variantClassName,
       checked && [
         'is-checked',
@@ -71,8 +72,7 @@ export const getBaseButtonClassNames = memoizeFunction((
           ':hover': styles.rootCheckedHovered,
           ':active': styles.rootCheckedPressed
         }
-      },
-      className
+      }
     ],
     flexContainer: [
       'ms-Button-flexContainer',
diff --git a/packages/office-ui-fabric-react/src/components/ComboBox/__snapshots__/ComboBox.test.tsx.snap b/packages/office-ui-fabric-react/src/components/ComboBox/__snapshots__/ComboBox.test.tsx.snap
index 88062f2cdcb1e6..a6f5bdf79bb210 100644
--- a/packages/office-ui-fabric-react/src/components/ComboBox/__snapshots__/ComboBox.test.tsx.snap
+++ b/packages/office-ui-fabric-react/src/components/ComboBox/__snapshots__/ComboBox.test.tsx.snap
@@ -163,8 +163,8 @@ exports[`ComboBox Renders ComboBox correctly 1`] = `
       checked={false}
       className=
           ms-Button
-          ms-Button--icon
           ms-ComboBox-CaretDown-button
+          ms-Button--icon
           {
             -moz-osx-font-smoothing: grayscale;
             -webkit-font-smoothing: antialiased;
diff --git a/packages/office-ui-fabric-react/src/components/Nav/__snapshots__/Nav.test.tsx.snap b/packages/office-ui-fabric-react/src/components/Nav/__snapshots__/Nav.test.tsx.snap
index eedb9cc7b26a88..7434557381e4b2 100644
--- a/packages/office-ui-fabric-react/src/components/Nav/__snapshots__/Nav.test.tsx.snap
+++ b/packages/office-ui-fabric-react/src/components/Nav/__snapshots__/Nav.test.tsx.snap
@@ -81,9 +81,9 @@ exports[`Nav renders Nav correctly 1`] = `
                 aria-pressed={undefined}
                 className=
                     ms-Button
+                    ms-Nav-link
                     ms-Button--action
                     ms-Button--command
-                    ms-Nav-link
                     {
                       -moz-osx-font-smoothing: grayscale;
                       -webkit-font-smoothing: antialiased;
@@ -128,6 +128,10 @@ exports[`Nav renders Nav correctly 1`] = `
                       top: 1px;
                       z-index: 1;
                     }
+                    .ms-Nav-compositeLink:hover & {
+                      background-color: #f8f8f8;
+                      color: #333333;
+                    }
                     &:hover {
                       color: #0078d7;
                     }
@@ -140,10 +144,6 @@ exports[`Nav renders Nav correctly 1`] = `
                     &:active .ms-Button-icon {
                       color: #004578;
                     }
-                    .ms-Nav-compositeLink:hover & {
-                      background-color: #f8f8f8;
-                      color: #333333;
-                    }
                 data-is-focusable={true}
                 disabled={undefined}
                 onClick={[Function]}
diff --git a/packages/office-ui-fabric-react/src/components/Pivot/__snapshots__/Pivot.test.tsx.snap b/packages/office-ui-fabric-react/src/components/Pivot/__snapshots__/Pivot.test.tsx.snap
index ed44a63d7761a2..900e43e349f3ee 100644
--- a/packages/office-ui-fabric-react/src/components/Pivot/__snapshots__/Pivot.test.tsx.snap
+++ b/packages/office-ui-fabric-react/src/components/Pivot/__snapshots__/Pivot.test.tsx.snap
@@ -24,11 +24,11 @@ exports[`Pivot renders Pivot correctly 1`] = `
         aria-selected={true}
         className=
             ms-Button
-            ms-Button--action
-            ms-Button--command
             ms-Pivot-link
             is-selected
             undefined
+            ms-Button--action
+            ms-Button--command
             {
               -moz-osx-font-smoothing: grayscale;
               -webkit-font-smoothing: antialiased;
@@ -120,9 +120,9 @@ exports[`Pivot renders Pivot correctly 1`] = `
         aria-selected={false}
         className=
             ms-Button
+            ms-Pivot-link
             ms-Button--action
             ms-Button--command
-            ms-Pivot-link
             {
               -moz-osx-font-smoothing: grayscale;
               -webkit-font-smoothing: antialiased;
diff --git a/packages/office-ui-fabric-react/src/components/SpinButton/__snapshots__/SpinButton.test.tsx.snap b/packages/office-ui-fabric-react/src/components/SpinButton/__snapshots__/SpinButton.test.tsx.snap
index d75698525e6eb2..a0050221b1b21f 100644
--- a/packages/office-ui-fabric-react/src/components/SpinButton/__snapshots__/SpinButton.test.tsx.snap
+++ b/packages/office-ui-fabric-react/src/components/SpinButton/__snapshots__/SpinButton.test.tsx.snap
@@ -154,8 +154,8 @@ exports[`SpinButton renders SpinButton correctly 1`] = `
         checked={false}
         className=
             ms-Button
-            ms-Button--icon
             ms-UpButton
+            ms-Button--icon
             {
               -moz-osx-font-smoothing: grayscale;
               -webkit-font-smoothing: antialiased;
@@ -259,8 +259,8 @@ exports[`SpinButton renders SpinButton correctly 1`] = `
         checked={false}
         className=
             ms-Button
-            ms-Button--icon
             ms-DownButton
+            ms-Button--icon
             {
               -moz-osx-font-smoothing: grayscale;
               -webkit-font-smoothing: antialiased;