diff --git a/.github/workflows/master-pr.yml b/.github/workflows/master-pr.yml
index 68076e0..1ae357a 100644
--- a/.github/workflows/master-pr.yml
+++ b/.github/workflows/master-pr.yml
@@ -35,7 +35,12 @@ jobs:
 
       - name: Compare versions
         run: |
-          if [ "$(printf '%s\n' "$PR_VERSION" "$MASTER_VERSION" | sort -V | head -n1)" = "$PR_VERSION" ] && [ "$PR_VERSION" != "$MASTER_VERSION" ]; then
+          if [ -z "$PR_VERSION" ] || [ -z "$MASTER_VERSION" ]; then
+            echo "One of the version variables is empty."
+            exit 1
+          fi
+
+          if [ "$(printf '%s\n' "$MASTER_VERSION" "$PR_VERSION" | sort -V | tail -n1)" != "$PR_VERSION" ] || [ "$PR_VERSION" = "$MASTER_VERSION" ]; then
             echo "Version in PR is not higher than master."
             exit 1
           else