diff --git a/dist/core.js b/dist/core.js
index e4c94df..ac8e785 100644
--- a/dist/core.js
+++ b/dist/core.js
@@ -19490,10 +19490,13 @@ function getLastCommitMessage(context) {
 }
 function loadCiEnv() {
   return __async(this, null, function* () {
-    const envCi = require_env_ci()();
+    let envCi = require_env_ci()();
     if (envCi.service == null) {
       throw new Error(`Unsupported CI service detected: ${envCi.service}`);
     }
+    if (envCi.isPr) {
+      envCi = __spreadProps(__spreadValues({}, envCi), { baseBranch: envCi.branch, branch: envCi.prBranch, prBranch: void 0 });
+    }
     if (envCi.branch == null) {
       const cmdOutput = yield exec.getExecOutput("git", ["rev-parse", "--abbrev-ref", "HEAD"]);
       envCi.branch = cmdOutput.stdout.trim();
diff --git a/packages/core/CHANGELOG.md b/packages/core/CHANGELOG.md
index 1f4959e..ac45b38 100644
--- a/packages/core/CHANGELOG.md
+++ b/packages/core/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 ## `1.0.1`
 
+* Fixed wrong branch detected for GitHub Actions `pull_request` builds
 * Fixed Git tags being matched that do not conform to semver
 
 ## `1.0.0`
diff --git a/packages/core/src/utils.ts b/packages/core/src/utils.ts
index f889232..d039a1a 100644
--- a/packages/core/src/utils.ts
+++ b/packages/core/src/utils.ts
@@ -171,11 +171,15 @@ export async function getLastCommitMessage(context: IContext): Promise<string |
  * @returns CI environment for the `context.ci` property
  */
 async function loadCiEnv(): Promise<any> {
-    const envCi = require("env-ci")();
+    let envCi = require("env-ci")();
     if (envCi.service == null) {
         throw new Error(`Unsupported CI service detected: ${envCi.service}`);
     }
 
+    if (envCi.isPr) {
+        // For PR builds, map `branch` (base) to `baseBranch` and `prBranch` (head) to `branch`
+        envCi = { ...envCi, baseBranch: envCi.branch, branch: envCi.prBranch, prBranch: undefined };
+    }
     if (envCi.branch == null) {
         const cmdOutput = await exec.getExecOutput("git", ["rev-parse", "--abbrev-ref", "HEAD"]);
         envCi.branch = cmdOutput.stdout.trim();