diff --git a/muzzle/src/main/java/io/opentelemetry/javaagent/tooling/HelperInjector.java b/muzzle/src/main/java/io/opentelemetry/javaagent/tooling/HelperInjector.java
index 4b042c02eb29..381d66a6ec06 100644
--- a/muzzle/src/main/java/io/opentelemetry/javaagent/tooling/HelperInjector.java
+++ b/muzzle/src/main/java/io/opentelemetry/javaagent/tooling/HelperInjector.java
@@ -7,7 +7,6 @@
 
 import static java.util.logging.Level.FINE;
 import static java.util.logging.Level.SEVERE;
-import static java.util.logging.Level.WARNING;
 
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import io.opentelemetry.instrumentation.api.internal.cache.Cache;
@@ -118,6 +117,7 @@ public HelperInjector(
 
     List<HelperClassDefinition> helpers =
         helperClassNames.stream()
+            .distinct()
             .map(
                 className ->
                     HelperClassDefinition.create(
@@ -184,11 +184,8 @@ public DynamicType.Builder<?> transform(
                           HelperClassDefinition::getClassName,
                           helper -> () -> helper.getBytecode().getBytecode(),
                           (a, b) -> {
-                            logger.log(
-                                WARNING,
-                                "Duplicate classname for helper class in module {0} detected",
-                                new Object[] {this.requestingName});
-                            return a;
+                            throw new IllegalStateException(
+                                "Duplicate classnames for helper class detected!");
                           },
                           LinkedHashMap::new));
 
diff --git a/testing-common/integration-tests/src/main/java/helper/DuplicateHelper.java b/testing-common/integration-tests/src/main/java/helper/DuplicateHelper.java
index 920d5b309ced..258e6bac73fd 100644
--- a/testing-common/integration-tests/src/main/java/helper/DuplicateHelper.java
+++ b/testing-common/integration-tests/src/main/java/helper/DuplicateHelper.java
@@ -1,3 +1,8 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 package helper;
 
 public class DuplicateHelper {
diff --git a/testing-common/integration-tests/src/main/java/helper/DuplicateHelperInstrumentation.java b/testing-common/integration-tests/src/main/java/helper/DuplicateHelperInstrumentation.java
index 478b0399ce02..4d6be67a1f9c 100644
--- a/testing-common/integration-tests/src/main/java/helper/DuplicateHelperInstrumentation.java
+++ b/testing-common/integration-tests/src/main/java/helper/DuplicateHelperInstrumentation.java
@@ -1,3 +1,8 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 package helper;
 
 import static net.bytebuddy.matcher.ElementMatchers.named;
diff --git a/testing-common/integration-tests/src/main/java/helper/DuplicateHelperInstrumentationModule.java b/testing-common/integration-tests/src/main/java/helper/DuplicateHelperInstrumentationModule.java
index 898acb496068..4b31e4fecc18 100644
--- a/testing-common/integration-tests/src/main/java/helper/DuplicateHelperInstrumentationModule.java
+++ b/testing-common/integration-tests/src/main/java/helper/DuplicateHelperInstrumentationModule.java
@@ -1,3 +1,8 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 package helper;
 
 import static java.util.Collections.singletonList;
diff --git a/testing-common/integration-tests/src/test/java/helper/DuplicateHelperTest.java b/testing-common/integration-tests/src/test/java/helper/DuplicateHelperTest.java
index 4b5dd877f0cb..b0aed068d476 100644
--- a/testing-common/integration-tests/src/test/java/helper/DuplicateHelperTest.java
+++ b/testing-common/integration-tests/src/test/java/helper/DuplicateHelperTest.java
@@ -1,3 +1,8 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 package helper;
 
 import static org.assertj.core.api.Assertions.assertThat;
diff --git a/testing-common/integration-tests/src/test/java/helper/DuplicateHelperTestClass.java b/testing-common/integration-tests/src/test/java/helper/DuplicateHelperTestClass.java
index 447029a4b7a9..6efbec4b0d22 100644
--- a/testing-common/integration-tests/src/test/java/helper/DuplicateHelperTestClass.java
+++ b/testing-common/integration-tests/src/test/java/helper/DuplicateHelperTestClass.java
@@ -1,3 +1,8 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 package helper;
 
 class DuplicateHelperTestClass {