diff --git a/source/app/action/index.mjs b/source/app/action/index.mjs
index 890681b1..5bc43aae 100644
--- a/source/app/action/index.mjs
+++ b/source/app/action/index.mjs
@@ -298,8 +298,19 @@
             //Merge pull request
               if (committer.merge) {
                 info("Merge method", committer.merge)
-                await committer.rest.pulls.merge({...github.context.repo, pull_number:number, merge_method:committer.merge})
-                info(`Merge #${number} to ${committer.branch}`, "ok")
+                do {
+                  //Check pull request mergeability (https://octokit.github.io/rest.js/v18#pulls-get)
+                    const {data:{mergeable, mergeable_state:state}} = await committer.rest.pulls.get({...github.context.repo, pull_number:number})
+                    console.debug(`Pull request #${number} mergeable state is "${state}"`)
+                    if (mergeable === null)
+                      continue
+                    if (!mergeable)
+                      throw new Error(`Pull request #${number} is not mergeable (state is "${state}")`)
+                  //Merge pull request
+                    await committer.rest.pulls.merge({...github.context.repo, pull_number:number, merge_method:committer.merge})
+                    info(`Merge #${number} to ${committer.branch}`, "ok")
+                    break
+                } while (true)
               }
           }