diff --git a/site/docs/skylark/backward-compatibility.md b/site/docs/skylark/backward-compatibility.md
index f157061b516804..91587aa2077c56 100644
--- a/site/docs/skylark/backward-compatibility.md
+++ b/site/docs/skylark/backward-compatibility.md
@@ -108,7 +108,7 @@ sorted(deps.to_list())  # recommended
 ```
 
 *   Flag: `--incompatible_depset_is_not_iterable`
-*   Default: `false`
+*   Default: `true`
 *   Tracking issue: [#5816](https://github.com/bazelbuild/bazel/issues/5816)
 
 
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 6c0e8365e2cb55..016924fc4e21a5 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
@@ -190,7 +190,7 @@ public class StarlarkSemanticsOptions extends OptionsBase implements Serializabl
 
   @Option(
       name = "incompatible_depset_is_not_iterable",
-      defaultValue = "false",
+      defaultValue = "true",
       documentationCategory = OptionDocumentationCategory.STARLARK_SEMANTICS,
       effectTags = {OptionEffectTag.BUILD_FILE_SEMANTICS},
       metadataTags = {
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 fcdd48b0ef4d11..22bdb2c09755f6 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
@@ -228,7 +228,7 @@ public static Builder builderWithDefaults() {
           .experimentalStarlarkConfigTransitions(true)
           .experimentalStarlarkUnusedInputsList(false)
           .incompatibleBzlDisallowLoadAfterStatement(true)
-          .incompatibleDepsetIsNotIterable(false)
+          .incompatibleDepsetIsNotIterable(true)
           .incompatibleDepsetUnion(true)
           .incompatibleDisableThirdPartyLicenseChecking(true)
           .incompatibleDisableDeprecatedAttrParams(true)