diff --git a/.github/workflows/ubuntu.yml b/.github/workflows/ubuntu.yml
index f3115b6..a96b5ed 100644
--- a/.github/workflows/ubuntu.yml
+++ b/.github/workflows/ubuntu.yml
@@ -186,6 +186,9 @@ jobs:
           - release: noble
             compiler_name: clang
             compiler_version: 20
+          - release: noble
+            compiler_name: clang
+            compiler_version: 21
     runs-on: ubuntu-24.04
     needs:
       - build
diff --git a/docker/ubuntu/Dockerfile b/docker/ubuntu/Dockerfile
index 598c25a..b668a6f 100644
--- a/docker/ubuntu/Dockerfile
+++ b/docker/ubuntu/Dockerfile
@@ -228,14 +228,21 @@ printf "%s\n" \
   "Acquire::AllowWeakRepositories \"true\";" \
   | tee /etc/apt/apt.conf.d/99llvm-allow-weak
 
-# Add LLVM repository for versions above 20 because it is not available in the default repo
-if [[ "${CLANG_VERSION}" -gt 20 ]]; then
+if [[ "${CLANG_VERSION}" -eq 21 ]]; then
   apt-get update
+    # Add LLVM repository for versions above 20 because it is not available in the default repo
   apt-get install -y --no-install-recommends lsb-release software-properties-common gnupg
   wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -
   DISTRO_CODENAME=$(lsb_release -cs)
   echo "deb http://apt.llvm.org/${DISTRO_CODENAME}/ llvm-toolchain-${DISTRO_CODENAME}-${CLANG_VERSION} main" \
     | tee /etc/apt/sources.list.d/llvm.list
+  apt-get update
+  apt-get install -y --no-install-recommends --allow-unauthenticated \
+    clang-tidy-${CLANG_VERSION}
+  update-alternatives \
+    --install /usr/bin/clang-tidy clang-tidy /usr/bin/clang-tidy-${CLANG_VERSION} 100
+  update-alternatives \
+    --install /usr/bin/run-clang-tidy run-clang-tidy /usr/bin/run-clang-tidy-${CLANG_VERSION} 100
   apt-get clean
   rm -rf /var/lib/apt/lists/*
 fi
@@ -245,7 +252,6 @@ apt-get install -y --no-install-recommends --allow-unauthenticated \
   clang-${CLANG_VERSION} \
   libclang-rt-${CLANG_VERSION}-dev \
   llvm-${CLANG_VERSION} \
-  clang-tidy-${CLANG_VERSION} \
   gcc \
   g++
 apt-get clean
@@ -259,10 +265,6 @@ update-alternatives \
   --slave /usr/bin/clang++ clang++ /usr/bin/clang++-${CLANG_VERSION}
 update-alternatives \
   --install /usr/bin/llvm-cov llvm-cov /usr/bin/llvm-cov-${CLANG_VERSION} 100
-update-alternatives \
-  --install /usr/bin/clang-tidy clang-tidy /usr/bin/clang-tidy-${CLANG_VERSION} 100
-update-alternatives \
-  --install /usr/bin/run-clang-tidy run-clang-tidy /usr/bin/run-clang-tidy-${CLANG_VERSION} 100
 update-alternatives --auto cc
 update-alternatives --auto c++
 update-alternatives --auto clang