diff --git a/src/main/java/io/cryostat/targets/TargetConnectionManager.java b/src/main/java/io/cryostat/targets/TargetConnectionManager.java
index 17b7791f2..b6d6c86b6 100644
--- a/src/main/java/io/cryostat/targets/TargetConnectionManager.java
+++ b/src/main/java/io/cryostat/targets/TargetConnectionManager.java
@@ -30,6 +30,7 @@
 import java.util.concurrent.Executor;
 import java.util.concurrent.Semaphore;
 
+import javax.management.InstanceNotFoundException;
 import javax.management.remote.JMXServiceURL;
 import javax.security.sasl.SaslException;
 
@@ -200,6 +201,8 @@ public <T> Uni<T> executeConnectedTaskUni(Target target, ConnectedTask<T> task)
                 .transform(t -> unwrapNestedException(RuntimeException.class, t))
                 .onFailure()
                 .invoke(logger::warn)
+                .onFailure(this::isInstanceNotFoundFailure)
+                .transform(t -> new HttpException(400, t))
                 .onFailure(this::isJmxAuthFailure)
                 .transform(t -> new HttpException(427, t))
                 .onFailure(this::isJmxSslFailure)
@@ -235,6 +238,8 @@ public <T> Uni<T> executeDirect(
                 .transform(t -> unwrapNestedException(RuntimeException.class, t))
                 .onFailure()
                 .invoke(logger::warn)
+                .onFailure(this::isInstanceNotFoundFailure)
+                .transform(t -> new HttpException(400, t))
                 .onFailure(this::isJmxAuthFailure)
                 .transform(t -> new HttpException(427, t))
                 .onFailure(this::isJmxSslFailure)
@@ -458,6 +463,15 @@ private boolean isServiceTypeFailure(Throwable t) {
                 && ExceptionUtils.indexOfType(e, SocketTimeoutException.class) >= 0;
     }
 
+    /** Check if the exception happened because an MBean was not found */
+    private boolean isInstanceNotFoundFailure(Throwable t) {
+        if (!(t instanceof Exception)) {
+            return false;
+        }
+        Exception e = (Exception) t;
+        return ExceptionUtils.indexOfType(e, InstanceNotFoundException.class) >= 0;
+    }
+
     @Name("io.cryostat.targets.TargetConnectionManager.TargetConnectionOpened")
     @Label("Target Connection Opened")
     @Category("Cryostat")