diff --git a/.github/actions/linux-build/action.yml b/.github/actions/linux-build/action.yml
index c607c6d02..ea448199e 100644
--- a/.github/actions/linux-build/action.yml
+++ b/.github/actions/linux-build/action.yml
@@ -76,7 +76,9 @@ runs:
           libboost-all-dev libbz2-dev libmysql++-dev \
           libreadline6-dev libssl-dev libtool openssl zlib1g-dev
         if [[ "$(lsb_release -sr)" == "26.04" ]]; then
-          sudo apt-get -y install libgoogle-perftools-dev default-libmysqlclient-dev
+          # libstdc++-16-dev: clang 21 links against the GCC 16 toolchain, the
+          # default g++ (GCC 15) only brings the GCC 15 C++ dev files
+          sudo apt-get -y install libgoogle-perftools-dev default-libmysqlclient-dev libstdc++-16-dev
         else
           sudo apt-get -y install google-perftools libmysqlclient-dev libncurses5-dev
         fi
diff --git a/apps/installer/includes/os_configs/ubuntu.sh b/apps/installer/includes/os_configs/ubuntu.sh
index 0ad9edd7f..deaa025ce 100644
--- a/apps/installer/includes/os_configs/ubuntu.sh
+++ b/apps/installer/includes/os_configs/ubuntu.sh
@@ -36,8 +36,11 @@ apt-get -y install ccache clang cmake curl make unzip jq screen tmux \
 
 # version-specific deps
 if [[ "$UBUNTU_VERSION" == "26.04" ]]; then
+  # libstdc++-16-dev: clang 21 links against the GCC 16 toolchain, while the
+  # default g++ is GCC 15 and only brings the GCC 15 C++ dev files, so cmake
+  # fails with "cannot find -lstdc++" without it.
   $SUDO DEBIAN_FRONTEND="noninteractive" \
-  apt-get -y install libgoogle-perftools-dev default-libmysqlclient-dev
+  apt-get -y install libgoogle-perftools-dev default-libmysqlclient-dev libstdc++-16-dev
 else
   $SUDO DEBIAN_FRONTEND="noninteractive" \
   apt-get -y install google-perftools libmysqlclient-dev libncurses5-dev libncursesw5-dev