diff --git a/.github/workflows/build-linux.yml b/.github/workflows/build-linux.yml
index afe328c3b..7553675c8 100644
--- a/.github/workflows/build-linux.yml
+++ b/.github/workflows/build-linux.yml
@@ -50,6 +50,8 @@ jobs:
         run: |
           # LLVM 9 is not in Bionic's repositories so we add the official LLVM repository.
           if [ "${{ matrix.compiler }}" = "clang" ] && [ "${{ matrix.version }}" = "9" ]; then
+            gpg --keyserver pool.sks-keyservers.net --recv-key 15CF4D18AF4F7421
+            gpg -a --export 15CF4D18AF4F7421 | sudo apt-key add -
             sudo add-apt-repository "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-9 main"
           fi
           sudo apt-get -y update
diff --git a/.github/workflows/build-python.yml b/.github/workflows/build-python.yml
index b8d6bc311..d4796e2bb 100644
--- a/.github/workflows/build-python.yml
+++ b/.github/workflows/build-python.yml
@@ -63,6 +63,8 @@ jobs:
         run: |
           # LLVM 9 is not in Bionic's repositories so we add the official LLVM repository.
           if [ "${{ matrix.compiler }}" = "clang" ] && [ "${{ matrix.version }}" = "9" ]; then
+            gpg --keyserver pool.sks-keyservers.net --recv-key 15CF4D18AF4F7421
+            gpg -a --export 15CF4D18AF4F7421 | sudo apt-key add -
             sudo add-apt-repository "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-9 main"
           fi
           sudo apt-get -y update
diff --git a/.github/workflows/build-special.yml b/.github/workflows/build-special.yml
index 648365f24..c314acb16 100644
--- a/.github/workflows/build-special.yml
+++ b/.github/workflows/build-special.yml
@@ -56,6 +56,8 @@ jobs:
         run: |
           # LLVM 9 is not in Bionic's repositories so we add the official LLVM repository.
           if [ "${{ matrix.compiler }}" = "clang" ] && [ "${{ matrix.version }}" = "9" ]; then
+            gpg --keyserver pool.sks-keyservers.net --recv-key 15CF4D18AF4F7421
+            gpg -a --export 15CF4D18AF4F7421 | sudo apt-key add -
             sudo add-apt-repository "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-9 main"
           fi
           sudo apt-get -y update