diff --git a/setup/README.md b/setup/README.md
index 055b07ab..7710b8ce 100644
--- a/setup/README.md
+++ b/setup/README.md
@@ -211,19 +211,35 @@ In contrast, a proper `boolean` input like `cabal-update` only accepts values `t
 
 ## Outputs
 
-| Name          | Description                                                                                                                | Type   |
-| ------------- | -------------------------------------------------------------------------------------------------------------------------- | ------ |
-| `ghc-path`    | The path of the ghc executable _directory_                                                                                 | string |
-| `cabal-path`  | The path of the cabal executable _directory_                                                                               | string |
-| `stack-path`  | The path of the stack executable _directory_                                                                               | string |
-| `cabal-store` | The path to the cabal store                                                                                                | string |
-| `stack-root`  | The path to the stack root (equal to the `STACK_ROOT` environment variable if it is set; otherwise an OS-specific default) | string |
-| `ghc-exe`     | The path of the ghc _executable_                                                                                           | string |
-| `cabal-exe`   | The path of the cabal _executable_                                                                                         | string |
-| `stack-exe`   | The path of the stack _executable_                                                                                         | string |
+The action outputs parameters for the components it installed.
+E.g. if `ghc-version: 8.10` is requested, the action will output `ghc-version: 8.10.7` if installation succeeded,
+according to the version resolution ()[src/versions.json].
+
+| Name            | Description                                                                                                                | Type   |
+| --------------- | -------------------------------------------------------------------------------------------------------------------------- | ------ |
+| `ghc-version`   | The resolved version of `ghc`                                                                                              | string |
+| `cabal-version` | The resolved version of `cabal`                                                                                            | string |
+| `stack-version` | The resolved version of `stack`                                                                                            | string |
+| `ghc-exe`       | The path of the `ghc` _executable_                                                                                         | string |
+| `cabal-exe`     | The path of the `cabal` _executable_                                                                                       | string |
+| `stack-exe`     | The path of the `stack` _executable_                                                                                       | string |
+| `ghc-path`      | The path of the `ghc` executable _directory_                                                                               | string |
+| `cabal-path`    | The path of the `cabal` executable _directory_                                                                             | string |
+| `stack-path`    | The path of the `stack` executable _directory_                                                                             | string |
+| `cabal-store`   | The path to the cabal store                                                                                                | string |
+| `stack-root`    | The path to the stack root (equal to the `STACK_ROOT` environment variable if it is set; otherwise an OS-specific default) | string |
 
 ## Version Support
 
+This action is conscious about the tool versions specified in [`versions.json`](src/versions.json).
+This list is replicated (hopefully correctly) below.
+
+Versions specified by the inputs, e.g. `ghc-version`, are resolved against this list,
+by taking the first entry from the list if `latest` is requested,
+or the first entry that is a (string-)extension of the requested version otherwise.
+E.g., `8.10` will be resolved to `8.10.7`, and so will `8.10.`, `8.` and `8`
+(and incorrectly, [even `8.1`](github.com/haskell/actions/issues/248)).
+
 **GHC:**
 
 - `latest` (default)
diff --git a/setup/__tests__/find-haskell.test.ts b/setup/__tests__/find-haskell.test.ts
index 4f1f023d..acd91933 100644
--- a/setup/__tests__/find-haskell.test.ts
+++ b/setup/__tests__/find-haskell.test.ts
@@ -67,13 +67,13 @@ describe('haskell/actions/setup', () => {
   });
 
   it('Versions resolve correctly', () => {
-    const v = {ghc: '8.6.5', cabal: '2.4.1.0', stack: '2.1.3'};
+    const v = {ghc: '8.6.5', cabal: '3.4.1.0', stack: '1.9.3'};
     forAllOS(os => {
       const options = getOpts(def(os), os, {
         'enable-stack': 'true',
-        'stack-version': '2.1',
+        'stack-version': '1',
         'ghc-version': '8.6',
-        'cabal-version': '2.4'
+        'cabal-version': '3.4'
       });
       forAllTools(t => expect(options[t].resolved).toBe(v[t]));
     });
@@ -96,6 +96,19 @@ describe('haskell/actions/setup', () => {
     });
   });
 
+  it('Versions resolve as string prefix (resolving 8.1 to 8.10.x should be considered a bug)', () => {
+    const v = {ghc: '8.10.7', cabal: '2.4.1.0', stack: '2.1.3'};
+    forAllOS(os => {
+      const options = getOpts(def(os), os, {
+        'enable-stack': 'true',
+        'stack-version': '2.1',
+        'ghc-version': '8.1',
+        'cabal-version': '2'
+      });
+      forAllTools(t => expect(options[t].resolved).toBe(v[t]));
+    });
+  });
+
   it('Enabling stack does not disable GHC or Cabal', () => {
     forAllOS(os => {
       const {ghc, cabal, stack} = getOpts(def(os), os, {