diff --git a/utils/config-utils/src/main/java/datadog/trace/config/inversion/ConfigHelper.java b/utils/config-utils/src/main/java/datadog/trace/config/inversion/ConfigHelper.java
index 59c183a4700..e58c71fa664 100644
--- a/utils/config-utils/src/main/java/datadog/trace/config/inversion/ConfigHelper.java
+++ b/utils/config-utils/src/main/java/datadog/trace/config/inversion/ConfigHelper.java
@@ -2,11 +2,14 @@
 
 import datadog.environment.EnvironmentVariables;
 import datadog.trace.api.telemetry.ConfigInversionMetricCollectorProvider;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -15,7 +18,7 @@ private ConfigHelper() {}
 
   /** Config Inversion strictness policy for enforcement of undocumented environment variables */
   public enum StrictnessPolicy {
-    STRICT,
+    STRICT_TEST,
     WARNING,
     TEST;
 
@@ -49,6 +52,9 @@ public String toString() {
   // Default to production source
   private SupportedConfigurationSource configSource = new SupportedConfigurationSource();
 
+  // Collects unsupported config keys encountered in STRICT_TEST mode
+  private final Set<String> unsupportedConfigs = ConcurrentHashMap.newKeySet();
+
   public static ConfigHelper get() {
     return INSTANCE;
   }
@@ -75,9 +81,18 @@ void resetCache() {
   void resetToDefaults() {
     configSource = new SupportedConfigurationSource();
     this.configInversionStrict = StrictnessPolicy.WARNING;
+    unsupportedConfigs.clear();
     resetCache();
   }
 
+  /** Returns and clears the set of unsupported config keys encountered in STRICT_TEST mode. */
+  public List<String> drainUnsupportedConfigs() {
+    List<String> result = new ArrayList<>(unsupportedConfigs);
+    unsupportedConfigs.clear();
+    Collections.sort(result);
+    return result;
+  }
+
   public static Map<String, String> env() {
     return get().getEnvironmentVariables();
   }
@@ -142,8 +157,13 @@ public String getEnvironmentVariable(String name) {
         ConfigInversionMetricCollectorProvider.get().setUndocumentedEnvVarMetric(name);
       }
 
-      if (configInversionStrict == StrictnessPolicy.STRICT) {
-        return null; // If strict mode is enabled, return null for unsupported configs
+      if (configInversionStrict == StrictnessPolicy.STRICT_TEST) {
+        unsupportedConfigs.add(name);
+        throw new IllegalArgumentException(
+            "Unsupported configuration: "
+                + name
+                + " is not in GeneratedSupportedConfigurations. "
+                + "Add it to metadata/supported-configurations.json or remove the usage.");
       }
     }
 
diff --git a/utils/config-utils/src/test/java/datadog/trace/config/inversion/ConfigHelperTest.java b/utils/config-utils/src/test/java/datadog/trace/config/inversion/ConfigHelperTest.java
index aed77304eac..9696642c8ac 100644
--- a/utils/config-utils/src/test/java/datadog/trace/config/inversion/ConfigHelperTest.java
+++ b/utils/config-utils/src/test/java/datadog/trace/config/inversion/ConfigHelperTest.java
@@ -62,7 +62,7 @@ static void setUp() {
             testSupported, testAliases, testAliasMapping, new HashMap<>());
     ConfigHelper.get().setConfigurationSource(testSource);
     strictness = ConfigHelper.get().configInversionStrictFlag();
-    ConfigHelper.get().setConfigInversionStrict(ConfigHelper.StrictnessPolicy.STRICT);
+    ConfigHelper.get().setConfigInversionStrict(ConfigHelper.StrictnessPolicy.STRICT_TEST);
   }
 
   @AfterAll
@@ -177,7 +177,7 @@ void testUnsupportedEnvWarningNotInTestMode() {
     assertEquals("banana", ConfigHelper.env("DD_FAKE_VAR"));
 
     // Cleanup
-    ConfigHelper.get().setConfigInversionStrict(ConfigHelper.StrictnessPolicy.STRICT);
+    ConfigHelper.get().setConfigInversionStrict(ConfigHelper.StrictnessPolicy.STRICT_TEST);
   }
 
   @Test