diff --git a/site/docs/skylark/backward-compatibility.md b/site/docs/skylark/backward-compatibility.md
index 9cd120aedce80f..f40fbde841f659 100644
--- a/site/docs/skylark/backward-compatibility.md
+++ b/site/docs/skylark/backward-compatibility.md
@@ -219,7 +219,7 @@ If you really want to override a value, use a separate statement:
 `mydict["a"] = 4`.
 
 *   Flag: `--incompatible_dict_literal_has_no_duplicates`
-*   Default: `false`
+*   Default: `true`
 
 
 ## Checked arithmetic
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemanticsOptions.java b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemanticsOptions.java
index 98dfb297c0a36c..89fabf6ab06681 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemanticsOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkSemanticsOptions.java
@@ -190,7 +190,7 @@ public class SkylarkSemanticsOptions extends OptionsBase implements Serializable
 
   @Option(
     name = "incompatible_dict_literal_has_no_duplicates",
-    defaultValue = "false",
+    defaultValue = "true",
     category = "incompatible changes",
     documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
     effectTags = {OptionEffectTag.UNKNOWN},