diff --git a/README.md b/README.md
index 6c5ba5e..583c6d5 100644
--- a/README.md
+++ b/README.md
@@ -88,6 +88,12 @@ steps:
       echo "CI_BASE_REF=$CI_BASE_REF"
       echo "CI_SHA_SHORT=$CI_SHA_SHORT"
       echo "CI_SHA=$CI_SHA"
+      echo "CI_PR_SHA_SHORT=$CI_PR_SHA_SHORT"
+      echo "CI_PR_SHA=$CI_PR_SHA"
+      echo "CI_PR_NUMBER=$CI_PR_NUMBER"
+      echo "CI_PR_ID=$CI_PR_ID"
+      echo "CI_PR_TITLE=$CI_PR_TITLE"
+      echo "CI_PR_DESCRIPTION=$CI_PR_DESCRIPTION"
       echo "CI_ACTOR=$CI_ACTOR"
       echo "CI_EVENT_NAME=$CI_EVENT_NAME"
       echo "CI_RUN_ID=$CI_RUN_ID"
diff --git a/dist/index.js b/dist/index.js
index 996f6c0..58b53bd 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -192,7 +192,7 @@ try {
   const pullRequest = github.context.payload &&
       github.context.payload.pull_request;
   if (pullRequest) {
-    const prSha = github.event.pull_request.head.sha;
+    const prSha = pullRequest.head.sha;
     core.exportVariable('CI_PR_SHA_SHORT', getShaShort(prSha));
     core.info(`Set CI_PR_SHA_SHORT=${process.env.CI_PR_SHA_SHORT}`);
 
@@ -215,7 +215,8 @@ try {
     core.info(`Set CI_PR_DESCRIPTION=${process.env.CI_PR_DESCRIPTION}`);
   } else {
     core.info('No pull request. ' +
-      'Cannot set "CI_PR_TITLE" and "CI_PR_DESCRIPTION".');
+      'Cannot set "CI_PR_SHA_SHORT", "CI_PR_SHA", "CI_PR_NUMBER", ' +
+      '"CI_PR_ID", "CI_PR_TITLE" and "CI_PR_DESCRIPTION".');
   }
 
   const actor = process.env.GITHUB_ACTOR;
diff --git a/index.js b/index.js
index 4830fd4..3b089f4 100644
--- a/index.js
+++ b/index.js
@@ -186,7 +186,7 @@ try {
   const pullRequest = github.context.payload &&
       github.context.payload.pull_request;
   if (pullRequest) {
-    const prSha = github.event.pull_request.head.sha;
+    const prSha = pullRequest.head.sha;
     core.exportVariable('CI_PR_SHA_SHORT', getShaShort(prSha));
     core.info(`Set CI_PR_SHA_SHORT=${process.env.CI_PR_SHA_SHORT}`);
 
@@ -209,7 +209,8 @@ try {
     core.info(`Set CI_PR_DESCRIPTION=${process.env.CI_PR_DESCRIPTION}`);
   } else {
     core.info('No pull request. ' +
-      'Cannot set "CI_PR_TITLE" and "CI_PR_DESCRIPTION".');
+      'Cannot set "CI_PR_SHA_SHORT", "CI_PR_SHA", "CI_PR_NUMBER", ' +
+      '"CI_PR_ID", "CI_PR_TITLE" and "CI_PR_DESCRIPTION".');
   }
 
   const actor = process.env.GITHUB_ACTOR;