diff --git a/packaging/aur/kst4contest-git/PKGBUILD b/packaging/aur/kst4contest-git/PKGBUILD
index 48e01732..48ba3981 100644
--- a/packaging/aur/kst4contest-git/PKGBUILD
+++ b/packaging/aur/kst4contest-git/PKGBUILD
@@ -7,12 +7,22 @@ arch=('x86_64')
 url="https://github.com/HamRadioOnline/kst4contest"
 license=('GPL-3.0-only')
 depends=('gst-plugins-base' 'gst-plugins-good')
-makedepends=('java-environment=21' 'git')
+makedepends=('git')
 provides=('kst4contest')
 conflicts=('kst4contest' 'kst4contest-bin')
 source=("kst4contest::git+https://github.com/HamRadioOnline/kst4contest.git")
 sha256sums=('SKIP')
 
+# The launcher is built with Temurin, not with the system JDK. Arch's openjdk links
+# jpackage's launcher library against the shared libstdc++, and that build aborts
+# with "pure virtual method called" (SIGABRT, core dump) in a static destructor when
+# the application exits; Temurin links libstdc++ statically, like the CI packages.
+# The _x86_64 arrays are deliberate: aur-publish.yml rewrites the plain sha256sums=
+# line on every release and would drop a second entry there.
+_temurin=21.0.13+9
+source_x86_64=("https://github.com/adoptium/temurin21-binaries/releases/download/jdk-${_temurin/+/%2B}/OpenJDK21U-jdk_x64_linux_hotspot_${_temurin/+/_}.tar.gz")
+sha256sums_x86_64=('d7f5d5cf865a2902b70ff549b97586a7d3f234e016f041ab447ea740c7d66d1c')
+
 pkgver() {
     cd "${srcdir}/kst4contest"
     BASE=$(grep -m1 '^version=' gradle.properties \
@@ -23,7 +33,7 @@ pkgver() {
 build() {
     cd "${srcdir}/kst4contest"
 
-    export JAVA_HOME=$(find /usr/lib/jvm -maxdepth 1 -name 'java-21-*' -type d | head -n 1)
+    export JAVA_HOME="${srcdir}/jdk-${_temurin}"
     export PATH="${JAVA_HOME}/bin:${PATH}"
 
     # A Gradle home inside $srcdir keeps the build independent of whatever the
@@ -31,7 +41,13 @@ build() {
     # cache, every dependency added since the last local build broke the package.
     export GRADLE_USER_HOME="${srcdir}/gradle-home"
 
-    ./gradlew --no-daemon -S :app-desktop:createDistributable
+    # The Java toolchain, and with it jpackage, would otherwise pick any JDK 21 it
+    # finds in /usr/lib/jvm, the system one included.
+    ./gradlew --no-daemon -S \
+        -Porg.gradle.java.installations.auto-detect=false \
+        -Porg.gradle.java.installations.auto-download=false \
+        -Porg.gradle.java.installations.paths="${JAVA_HOME}" \
+        :app-desktop:createDistributable
 
     # package() reads dist/KST4Contest. Application name, icon and the JDK
     # module list come from app-desktop/build.gradle.kts.
diff --git a/packaging/aur/kst4contest/PKGBUILD b/packaging/aur/kst4contest/PKGBUILD
index b647d8bd..6e79b5d3 100644
--- a/packaging/aur/kst4contest/PKGBUILD
+++ b/packaging/aur/kst4contest/PKGBUILD
@@ -7,16 +7,25 @@ arch=('x86_64')
 url="https://github.com/HamRadioOnline/kst4contest"
 license=('GPL-3.0-only')
 depends=('gst-plugins-base' 'gst-plugins-good')
-makedepends=('java-environment=21')
 provides=('kst4contest')
 conflicts=('kst4contest-bin' 'kst4contest-git')
 source=("${pkgname}-${pkgver}.tar.gz::https://github.com/HamRadioOnline/kst4contest/archive/refs/tags/v${pkgver}.tar.gz")
 sha256sums=('e702df24a29e6f914a43934df0095bc4adbd00a9f02df3a632816c832272e914')
 
+# The launcher is built with Temurin, not with the system JDK. Arch's openjdk links
+# jpackage's launcher library against the shared libstdc++, and that build aborts
+# with "pure virtual method called" (SIGABRT, core dump) in a static destructor when
+# the application exits; Temurin links libstdc++ statically, like the CI packages.
+# The _x86_64 arrays are deliberate: aur-publish.yml rewrites the plain sha256sums=
+# line on every release and would drop a second entry there.
+_temurin=21.0.13+9
+source_x86_64=("https://github.com/adoptium/temurin21-binaries/releases/download/jdk-${_temurin/+/%2B}/OpenJDK21U-jdk_x64_linux_hotspot_${_temurin/+/_}.tar.gz")
+sha256sums_x86_64=('d7f5d5cf865a2902b70ff549b97586a7d3f234e016f041ab447ea740c7d66d1c')
+
 build() {
     cd "${srcdir}/kst4contest-${pkgver}"
 
-    export JAVA_HOME=$(find /usr/lib/jvm -maxdepth 1 -name 'java-21-*' -type d | head -n 1)
+    export JAVA_HOME="${srcdir}/jdk-${_temurin}"
     export PATH="${JAVA_HOME}/bin:${PATH}"
 
     # A Gradle home inside $srcdir keeps the build independent of whatever the
@@ -24,7 +33,13 @@ build() {
     # cache, every dependency added since the last local build broke the package.
     export GRADLE_USER_HOME="${srcdir}/gradle-home"
 
-    ./gradlew --no-daemon -S :app-desktop:createDistributable
+    # The Java toolchain, and with it jpackage, would otherwise pick any JDK 21 it
+    # finds in /usr/lib/jvm, the system one included.
+    ./gradlew --no-daemon -S \
+        -Porg.gradle.java.installations.auto-detect=false \
+        -Porg.gradle.java.installations.auto-download=false \
+        -Porg.gradle.java.installations.paths="${JAVA_HOME}" \
+        :app-desktop:createDistributable
 
     # package() reads dist/KST4Contest. Application name, icon and the JDK
     # module list come from app-desktop/build.gradle.kts, so this PKGBUILD no