diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..be00eaa
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,25 @@
+name: Build and run tests
+
+on:
+  pull_request:
+
+jobs:
+  BuildAndTest:
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v1
+
+      - name: Cache Swift packages
+        uses: actions/cache@v2
+        with:
+          path: |
+              .build/checkouts
+              .build/repositories
+              .build/workspace-state.json
+          key: ${{ runner.os }}-${{ hashFiles('Package.resolved') }}
+
+      - name: Build
+        run: swift build
+
+      - name: Run tests
+        run: swift test
diff --git a/Sources/LibMakeColors/MakeColors.swift b/Sources/LibMakeColors/MakeColors.swift
index b125ec4..8dfa743 100644
--- a/Sources/LibMakeColors/MakeColors.swift
+++ b/Sources/LibMakeColors/MakeColors.swift
@@ -76,7 +76,8 @@ public final class MakeColors: ParsableCommand, Context {
         if let output = output {
             return URL(fileURLWithPath: output)
         } else {
-            return URL(fileURLWithPath: input).deletingPathExtension().appendingPathExtension(`extension`)
+            let basename = URL(fileURLWithPath: input).deletingPathExtension().lastPathComponent
+            return URL(fileURLWithPath: basename).appendingPathExtension(`extension`)
         }
     }
 }