diff --git a/controller/src/main/java/org/jboss/as/controller/ControllerMessages.java b/controller/src/main/java/org/jboss/as/controller/ControllerMessages.java
index 620205801308..af04199435d9 100644
--- a/controller/src/main/java/org/jboss/as/controller/ControllerMessages.java
+++ b/controller/src/main/java/org/jboss/as/controller/ControllerMessages.java
@@ -49,6 +49,8 @@
 import org.jboss.logging.annotations.MessageBundle;
 import org.jboss.logging.annotations.Param;
 import org.jboss.modules.ModuleIdentifier;
+import org.jboss.modules.ModuleLoadException;
+import org.jboss.modules.ModuleNotFoundException;
 import org.jboss.msc.service.ServiceName;
 import org.jboss.msc.service.StartException;
 
@@ -2648,4 +2650,10 @@ public interface ControllerMessages {
     @Message(id = 13452, value = "Legacy extension '%s' is not supported on servers running this version. The extension " +
             "is only supported for use by hosts running a previous release in a mixed-version managed domain")
     String unsupportedLegacyExtension(String extensionName);
+
+    @Message(id = 13453, value = "Extension module %s not found")
+    OperationFailedException extensionModuleNotFound(@Cause ModuleNotFoundException cause, String module);
+
+    @Message(id = 13454, value = "Failed to load Extension module %s")
+    RuntimeException extensionModuleLoadingFailure(@Cause ModuleLoadException cause, String module);
 }
diff --git a/controller/src/main/java/org/jboss/as/controller/extension/ExtensionAddHandler.java b/controller/src/main/java/org/jboss/as/controller/extension/ExtensionAddHandler.java
index 11ac8fa610af..e6a5eabd98b1 100644
--- a/controller/src/main/java/org/jboss/as/controller/extension/ExtensionAddHandler.java
+++ b/controller/src/main/java/org/jboss/as/controller/extension/ExtensionAddHandler.java
@@ -21,6 +21,7 @@
 import static org.jboss.as.controller.descriptions.ModelDescriptionConstants.ADD;
 import static org.jboss.as.controller.descriptions.ModelDescriptionConstants.OP_ADDR;
 
+import org.jboss.as.controller.ControllerMessages;
 import org.jboss.as.controller.Extension;
 import org.jboss.as.controller.OperationContext;
 import org.jboss.as.controller.OperationFailedException;
@@ -30,6 +31,7 @@
 import org.jboss.modules.Module;
 import org.jboss.modules.ModuleIdentifier;
 import org.jboss.modules.ModuleLoadException;
+import org.jboss.modules.ModuleNotFoundException;
 
 /**
  * Base handler for the extension resource add operation.
@@ -49,7 +51,7 @@ public class ExtensionAddHandler implements OperationStepHandler {
      * Create the AbstractAddExtensionHandler
      * @param extensionRegistry registry for extensions
      * @param parallelBoot {@code true} is parallel initialization of extensions is in progress; {@code false} if not
-     * @param slaveHC
+     * @param slaveHC {@code true} if this handler will execute in a slave HostController
      */
     public ExtensionAddHandler(final ExtensionRegistry extensionRegistry, final boolean parallelBoot, boolean standalone, boolean slaveHC) {
         assert extensionRegistry != null : "extensionRegistry is null";
@@ -97,8 +99,14 @@ void initializeExtension(String module) throws OperationFailedException {
                     SecurityActions.setThreadContextClassLoader(oldTccl);
                 }
             }
+        } catch (ModuleNotFoundException e) {
+            // Treat this as a user mistake, e.g. incorrect module name.
+            // Throw OFE so post-boot it only gets logged at DEBUG.
+            throw ControllerMessages.MESSAGES.extensionModuleNotFound(e, module);
         } catch (ModuleLoadException e) {
-            throw new OperationFailedException(new ModelNode().set(e.toString()));
+            // The module is there but can't be loaded. Treat this as an internal problem.
+            // Throw a runtime exception so it always gets logged at ERROR in the server log with stack trace details.
+            throw ControllerMessages.MESSAGES.extensionModuleLoadingFailure(e, module);
         }
     }