diff --git a/src/main/java/com/google/devtools/build/lib/packages/StarlarkSemanticsOptions.java b/src/main/java/com/google/devtools/build/lib/packages/StarlarkSemanticsOptions.java
index 369774e..0bab4bf 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/StarlarkSemanticsOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/StarlarkSemanticsOptions.java
@@ -333,7 +333,7 @@
   /** Controls legacy arguments to ctx.actions.Args#add. */
   @Option(
       name = "incompatible_disallow_old_style_args_add",
-      defaultValue = "false",
+      defaultValue = "true",
       category = "incompatible changes",
       documentationCategory = OptionDocumentationCategory.STARLARK_SEMANTICS,
       effectTags = {OptionEffectTag.BUILD_FILE_SEMANTICS},
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/StarlarkSemantics.java b/src/main/java/com/google/devtools/build/lib/syntax/StarlarkSemantics.java
index 87ae5ce..4b01e23 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/StarlarkSemantics.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/StarlarkSemantics.java
@@ -221,7 +221,7 @@
           .incompatibleDisallowLegacyJavaProvider(false)
           .incompatibleDisallowLegacyJavaInfo(false)
           .incompatibleDisallowLoadLabelsToCrossPackageBoundaries(false)
-          .incompatibleDisallowOldStyleArgsAdd(false)
+          .incompatibleDisallowOldStyleArgsAdd(true)
           .incompatibleDisallowStructProviderSyntax(false)
           .incompatibleExpandDirectories(true)
           .incompatibleNewActionsApi(false)