diff --git a/containers/debian/base.Dockerfile b/containers/debian/base.Dockerfile
index 1542bfbdba5aa03803775b64c69e770da735ecda..1b6547c4ea060551bda6640830308e157f647cca 100644
--- a/containers/debian/base.Dockerfile
+++ b/containers/debian/base.Dockerfile
@@ -90,9 +90,13 @@ case ${ID} in
   *) echo "Unsupported ID=${ID}" ; exit 1 ;;
 esac
 # Clang version and repository
-CLANG="-14"
+CLANG="-16"
 curl -s https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -
-echo "deb http://apt.llvm.org/${VERSION_CODENAME} llvm-toolchain-${VERSION_CODENAME}${CLANG} main" > /etc/apt/source.list.d/llvm.list
+if [ ${VERSION_CODENAME} = trixie ] ; then
+  echo "deb http://apt.llvm.org/unstable llvm-toolchain${CLANG} main" > /etc/apt/sources.list.d/llvm.list
+else
+  echo "deb http://apt.llvm.org/${VERSION_CODENAME} llvm-toolchain-${VERSION_CODENAME}${CLANG} main" > /etc/apt/sources.list.d/llvm.list
+fi
 # Install packages
 apt-get -yqq update
 apt-get -yqq install gcc${GCC} g++${GCC} gfortran${GCC}
diff --git a/spack-environment/packages.yaml b/spack-environment/packages.yaml
index 1086d1f11b25781620c5dc85a728884a4d0ae53b..fe6a1f60e14025793ef1258ddaa8d5174c48fe19 100644
--- a/spack-environment/packages.yaml
+++ b/spack-environment/packages.yaml
@@ -144,7 +144,7 @@ packages:
     - '@1.0.7'
   iwyu:
     require:
-    - '@0.18'
+    - '@0.20'
   jana2:
     require:
     - '@2.1.2'
diff --git a/spack.sh b/spack.sh
index 8603a7ecaf8e617e645468e52836065c50dfdfd4..db3602d86a9b855744f31a4a20b4d0a783d2420f 100644
--- a/spack.sh
+++ b/spack.sh
@@ -59,6 +59,7 @@ e1373d5408170047626583916db02911585c133a
 a65f13f79f617b6aa0b235aa5db612473b6d8c0e
 ed8ecc469e7b87842a876323878831e301f136a2
 4991a60eacb5df289383f755e40702b720ed0513
+c485709f625429a88a184a099373d76c9438f8e3
 ---
 ## Ref: https://github.com/spack/spack/commit/[hash]
 ## [hash]: [description]
@@ -117,3 +118,4 @@ ed8ecc469e7b87842a876323878831e301f136a2
 ## a65f13f79f617b6aa0b235aa5db612473b6d8c0e: root: add latest available tag
 ## ed8ecc469e7b87842a876323878831e301f136a2: podio: Add the latest tag (0.17.2)
 ## 4991a60eacb5df289383f755e40702b720ed0513: podio: Add latest tag 0.17.3
+## c485709f625429a88a184a099373d76c9438f8e3: iwyu: new versions up 0.21 (depends_on llvm-17)