diff --git a/README.md b/README.md
index fc44f15..e31b467 100644
--- a/README.md
+++ b/README.md
@@ -53,6 +53,10 @@ All inputs are optional.
   <td><code>components</code></td>
   <td>Comma-separated string of additional components to install e.g. <code>clippy, rustfmt</code></td>
 </tr>
+<tr>
+  <td><code>set-default</code></td>
+  <td>Whether to set the installed toolchain as the active default via <code>rustup default &lt;toolchain&gt;</code>. Defaults to <code>true</code>. Set to <code>false</code> if you only plan to use the toolchain with explicit <code>+toolchain</code> overrides in your commands and don't want to change the runner's global default.</td>
+</tr>
 </table>
 
 <br>
diff --git a/action.yml b/action.yml
index b48984a..ef8c015 100644
--- a/action.yml
+++ b/action.yml
@@ -18,6 +18,10 @@ inputs:
   components:
     description: Comma-separated list of components to be additionally installed
     required: false
+  set-default:
+    description: Whether to set the installed toolchain as the rustup default (rustup default <toolchain>)
+    required: false
+    default: 'true'
 
 outputs:
   cachekey:
@@ -94,6 +98,7 @@ runs:
       shell: bash
 
     - run: rustup default ${{steps.parse.outputs.toolchain}}
+      if: ${{inputs['set-default'] == 'true'}}
       shell: bash
       continue-on-error: true  # https://github.com/dtolnay/rust-toolchain/issues/127