diff --git a/src/index.js b/src/index.js
index cc821fd47..cf1590a51 100644
--- a/src/index.js
+++ b/src/index.js
@@ -58,7 +58,17 @@ module.exports = async function run() {
             per_page: 2
           });
 
-          if (commits.length === 1) {
+          // GitHub does not count merge commits when deciding whether to use
+          // the PR title or a commit message for the squash commit message.
+          const nonMergeCommits = commits.filter(
+            (commit) => !commit.message.startsWith('Merge branch')
+          );
+
+          // If there is only one (non merge) commit present, GitHub will use
+          // that commit rather than the PR title for the title of a squash
+          // commit. To make sure a semantic title is used for the squash
+          // commit, we need to validate the commit title.
+          if (nonMergeCommits.length === 1) {
             try {
               await validatePrTitle(commits[0].commit.message, {
                 types,