diff --git a/.github/workflows/linux.yml b/.github/workflows/linux.yml
index 7e05f80a..6d88ae3c 100644
--- a/.github/workflows/linux.yml
+++ b/.github/workflows/linux.yml
@@ -112,13 +112,13 @@ jobs:
         set -x
         source /etc/os-release
         wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
-        sudo add-apt-repository "deb http://apt.llvm.org/${UBUNTU_CODENAME}/ llvm-toolchain-${UBUNTU_CODENAME}-14 main"
+        sudo add-apt-repository "deb http://apt.llvm.org/${UBUNTU_CODENAME}/ llvm-toolchain-${UBUNTU_CODENAME}-15 main"
         sudo apt-get update  # due to new repository
         # NOTE: Please note the version-specific ${PATH} extension for Clang in .travis.sh
         sudo apt-get install --yes --no-install-recommends -V \
-            clang-14 \
-            clang-format-14 \
-            llvm-14
+            clang-15 \
+            clang-format-15 \
+            llvm-15
     - name: Install build dependencies (common)
       run: |-
         sudo apt-get install --yes --no-install-recommends -V \
diff --git a/.travis.sh b/.travis.sh
index 79430ed8..bb69e80f 100755
--- a/.travis.sh
+++ b/.travis.sh
@@ -39,7 +39,7 @@ if [[ ${TRAVIS_OS_NAME} = osx ]]; then
     export PATH="/usr/local/opt/coreutils/libexec/gnubin${PATH:+:}${PATH}"
     export PATH="/usr/local/opt/findutils/libexec/gnubin${PATH:+:}${PATH}"
 elif [[ ${TRAVIS_OS_NAME} = linux ]]; then
-    export PATH="/usr/lib/llvm-14/bin:${PATH}"
+    export PATH="/usr/lib/llvm-15/bin:${PATH}"
 fi
 
 echo "New \${PATH}:"
diff --git a/expat/Changes b/expat/Changes
index ccfdbc19..a57f0981 100644
--- a/expat/Changes
+++ b/expat/Changes
@@ -35,10 +35,12 @@ Release x.x.x xxx xxxxx xx xxxx
        #626 #641  Stop exporting API symbols when building a static library
             #620  CMake: Make documentation on variables a bit more consistent
             #610  Address Cppcheck 2.8.1 warning
+            #643  Address Clang 15 compiler warnings
 
         Infrastructure:
        #597 #598  CI: Windows: Start covering MSVC 2022
             #632  CI: Linux: Make migration off deprecated Ubuntu 18.04 work
+            #643  CI: Upgrade Clang from 14 to 15
 
         Special thanks to:
             David Faure
diff --git a/expat/tests/runtests.c b/expat/tests/runtests.c
index ab3aff65..9a1dc934 100644
--- a/expat/tests/runtests.c
+++ b/expat/tests/runtests.c
@@ -11836,12 +11836,12 @@ START_TEST(test_accounting_precision) {
 END_TEST
 
 static float
-portableNAN() {
+portableNAN(void) {
   return strtof("nan", NULL);
 }
 
 static float
-portableINFINITY() {
+portableINFINITY(void) {
   return strtof("infinity", NULL);
 }