diff --git a/quarkus/dist/src/main/content/bin/kc.bat b/quarkus/dist/src/main/content/bin/kc.bat
index bda2ac5bc1..c9c7ad5721 100644
--- a/quarkus/dist/src/main/content/bin/kc.bat
+++ b/quarkus/dist/src/main/content/bin/kc.bat
@@ -165,7 +165,8 @@ if "x%JAVA%" == "x" (
 
 set CLASSPATH_OPTS="%DIRNAME%..\lib\quarkus-run.jar"
 
-set JAVA_RUN_OPTS=%JAVA_OPTS% -Dkc.home.dir="%DIRNAME%.." -Djboss.server.config.dir="%DIRNAME%..\conf" -Dkeycloak.theme.dir="%DIRNAME%..\themes" %SERVER_OPTS% -cp %CLASSPATH_OPTS% io.quarkus.bootstrap.runner.QuarkusEntryPoint %CONFIG_ARGS%
+rem The property 'java.util.concurrent.ForkJoinPool.common.threadFactory' is set here, as a Java Agent or enabling JMX might initialize the factory before Quarkus can set the property in JDK21+.
+set JAVA_RUN_OPTS=-Djava.util.concurrent.ForkJoinPool.common.threadFactory=io.quarkus.bootstrap.forkjoin.QuarkusForkJoinWorkerThreadFactory %JAVA_OPTS% -Dkc.home.dir="%DIRNAME%.." -Djboss.server.config.dir="%DIRNAME%..\conf" -Dkeycloak.theme.dir="%DIRNAME%..\themes" %SERVER_OPTS% -cp %CLASSPATH_OPTS% io.quarkus.bootstrap.runner.QuarkusEntryPoint %CONFIG_ARGS%
 
 set OPTIMIZED_OPTION=--optimized
 set HELP_LONG_OPTION=--help
diff --git a/quarkus/dist/src/main/content/bin/kc.sh b/quarkus/dist/src/main/content/bin/kc.sh
index 597647767c..5b3d53324a 100644
--- a/quarkus/dist/src/main/content/bin/kc.sh
+++ b/quarkus/dist/src/main/content/bin/kc.sh
@@ -157,7 +157,8 @@ esceval_args() {
 
 JAVA_RUN_OPTS=$(echo "$JAVA_OPTS" | xargs printf '%s\n' | esceval_args)
 
-JAVA_RUN_OPTS="$JAVA_RUN_OPTS $SERVER_OPTS -cp $CLASSPATH_OPTS io.quarkus.bootstrap.runner.QuarkusEntryPoint ${CONFIG_ARGS#?}"
+# The property 'java.util.concurrent.ForkJoinPool.common.threadFactory' is set here, as a Java Agent or enabling JMX might initialize the factory before Quarkus can set the property in JDK21+.
+JAVA_RUN_OPTS="-Djava.util.concurrent.ForkJoinPool.common.threadFactory=io.quarkus.bootstrap.forkjoin.QuarkusForkJoinWorkerThreadFactory $JAVA_RUN_OPTS $SERVER_OPTS -cp $CLASSPATH_OPTS io.quarkus.bootstrap.runner.QuarkusEntryPoint ${CONFIG_ARGS#?}"
 
 if [ "$PRINT_ENV" = "true" ]; then
   echo "Using JAVA_OPTS: $JAVA_OPTS"
diff --git a/quarkus/runtime/src/main/java/org/keycloak/quarkus/runtime/KeycloakMain.java b/quarkus/runtime/src/main/java/org/keycloak/quarkus/runtime/KeycloakMain.java
index 980684190b..9a4e05a64d 100644
--- a/quarkus/runtime/src/main/java/org/keycloak/quarkus/runtime/KeycloakMain.java
+++ b/quarkus/runtime/src/main/java/org/keycloak/quarkus/runtime/KeycloakMain.java
@@ -29,6 +29,7 @@ import static org.keycloak.quarkus.runtime.cli.command.Start.isDevProfileNotAllo
 import java.io.PrintWriter;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.ForkJoinPool;
 
 import jakarta.enterprise.context.ApplicationScoped;
 import org.keycloak.common.profile.ProfileException;
@@ -56,6 +57,8 @@ import io.quarkus.runtime.annotations.QuarkusMain;
 public class KeycloakMain implements QuarkusApplication {
 
     public static void main(String[] args) {
+        ensureForkJoinPoolThreadFactoryHasBeenSetToQuarkus();
+
         System.setProperty("kc.version", Version.VERSION);
         List<String> cliArgs = null;
         try {
@@ -96,6 +99,25 @@ public class KeycloakMain implements QuarkusApplication {
         parseAndRun(cliArgs);
     }
 
+    /**
+     * Verify that the property for the ForkJoinPool factory set by Quarkus matches the actual factory.
+     * If this is not the case, the classloader for those threads is not set correctly, and for example loading configurations
+     * via SmallRye is unreliable. This can happen if a Java Agent or JMX initializes the ForkJoinPool before Java's main method is run.
+     */
+    private static void ensureForkJoinPoolThreadFactoryHasBeenSetToQuarkus() {
+        // At this point, the settings from the CLI are no longer visible as they have been overwritten in the QuarkusEntryPoint.
+        // Therefore, the only thing we can do is to check if the thread pool class name is the same as in the configuration.
+        final String FORK_JOIN_POOL_COMMON_THREAD_FACTORY = "java.util.concurrent.ForkJoinPool.common.threadFactory";
+        String sf = System.getProperty(FORK_JOIN_POOL_COMMON_THREAD_FACTORY);
+        //noinspection resource
+        if (!ForkJoinPool.commonPool().getFactory().getClass().getName().equals(sf)) {
+            Logger.getLogger(KeycloakMain.class).errorf("The ForkJoinPool has been initialized with the wrong thread factory. The property '%s' should be set on the Java CLI to ensure Java's ForkJoinPool will always be initialized with '%s' even if there are Java agents which might initialize logging or other capabilities earlier than the main method.",
+                    FORK_JOIN_POOL_COMMON_THREAD_FACTORY,
+                    sf);
+            throw new RuntimeException("The ForkJoinPool has been initialized with the wrong thread factory");
+        }
+    }
+
     private static void handleUsageError(String message) {
         handleUsageError(message, null);
     }
diff --git a/quarkus/tests/integration/pom.xml b/quarkus/tests/integration/pom.xml
index 1876cbaa77..bd2901ffa0 100644
--- a/quarkus/tests/integration/pom.xml
+++ b/quarkus/tests/integration/pom.xml
@@ -114,7 +114,7 @@
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-surefire-plugin</artifactId>
                 <configuration>
-                    <argLine>-Djdk.net.hosts.file=${project.build.testOutputDirectory}/hosts_file -XX:+ExitOnOutOfMemoryError -XX:+HeapDumpOnOutOfMemoryError --add-opens=java.base/java.security=ALL-UNNAMED</argLine>
+                    <argLine>-Djdk.net.hosts.file=${project.build.testOutputDirectory}/hosts_file -XX:+ExitOnOutOfMemoryError -XX:+HeapDumpOnOutOfMemoryError --add-opens=java.base/java.security=ALL-UNNAMED -Djava.util.concurrent.ForkJoinPool.common.threadFactory=io.quarkus.bootstrap.forkjoin.QuarkusForkJoinWorkerThreadFactory</argLine>
                     <systemPropertyVariables>
                         <kc.quarkus.tests.dist>${kc.quarkus.tests.dist}</kc.quarkus.tests.dist>
                     </systemPropertyVariables>