diff --git a/.github/workflows/api_doc_build.yml b/.github/workflows/api_doc_build.yml
index 53334db3..f7b4f0f0 100644
--- a/.github/workflows/api_doc_build.yml
+++ b/.github/workflows/api_doc_build.yml
@@ -10,7 +10,7 @@ env:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
 
     steps:
     - uses: actions/checkout@v2