diff --git a/.github/workflows/R-CMD-check.yaml b/.github/workflows/R-CMD-check.yaml
index 8a12fe0..22db66e 100644
--- a/.github/workflows/R-CMD-check.yaml
+++ b/.github/workflows/R-CMD-check.yaml
@@ -1,10 +1,10 @@
+# Workflow derived from https://github.com/r-lib/actions/tree/v2/examples
+
 on:
   push:
-    branches: 
-    - main
+    branches: [main, master]
   pull_request:
-    branches: 
-    - main
+    branches: [main, master]
 
 name: R-CMD-check
 
@@ -18,11 +18,10 @@ jobs:
       fail-fast: false
       matrix:
         config:
-          - {os: macos-latest,   r: 'devel'}
-          - {os: macos-latest,   r: 'release'}
+          - {os: macOS-latest,   r: 'devel'}
+          - {os: macOS-latest,   r: 'release'}
+          - {os: windows-latest, r: 'devel'}
           - {os: windows-latest, r: 'release'}
-          - {os: windows-latest, r: '3.6'} # Use 3.6 to trigger usage of RTools35
-          - {os: windows-latest, r: '4.1'} # use 4.1 to check with rtools40's older compiler
           - {os: ubuntu-latest,  r: 'devel', http-user-agent: 'release'}
           - {os: ubuntu-latest,  r: 'release'}
           - {os: ubuntu-latest,  r: 'oldrel'}