diff --git a/.gitea/workflows/ci.yaml b/.gitea/workflows/ci.yaml
index f5700d6..5af2493 100644
--- a/.gitea/workflows/ci.yaml
+++ b/.gitea/workflows/ci.yaml
@@ -4,6 +4,11 @@ on:
   push:
     branches: ["**"]
 
+# One build at a time on the shared runner: a second run waits for the first.
+concurrency:
+  group: gites-build
+  cancel-in-progress: false
+
 jobs:
   check:
     runs-on: ubuntu-latest
diff --git a/.gitea/workflows/release.yaml b/.gitea/workflows/release.yaml
index 7ffa912..92ba27b 100644
--- a/.gitea/workflows/release.yaml
+++ b/.gitea/workflows/release.yaml
@@ -9,6 +9,11 @@ on:
 permissions:
   contents: write
 
+# One build at a time on the shared runner: a second run waits for the first.
+concurrency:
+  group: gites-build
+  cancel-in-progress: false
+
 jobs:
   release:
     runs-on: ubuntu-latest