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 ead4ea6dee1bc8..7d621b0a3ed893 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
@@ -496,7 +496,7 @@ public class StarlarkSemanticsOptions extends OptionsBase implements Serializabl
 
   @Option(
       name = "incompatible_remap_main_repo",
-      defaultValue = "false",
+      defaultValue = "true",
       documentationCategory = OptionDocumentationCategory.STARLARK_SEMANTICS,
       effectTags = OptionEffectTag.LOADING_AND_ANALYSIS,
       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 dec278e0ea2db0..03927c0c2dce80 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
@@ -270,7 +270,7 @@ public static Builder builderWithDefaults() {
           .incompatibleNoRuleOutputsParam(false)
           .incompatibleNoSupportToolsInActionInputs(true)
           .incompatibleNoTargetOutputGroup(true)
-          .incompatibleRemapMainRepo(false)
+          .incompatibleRemapMainRepo(true)
           .incompatibleRemoveNativeMavenJar(false)
           .incompatibleRunShellCommandString(false)
           .incompatibleRestrictNamedParams(true)
diff --git a/src/test/java/com/google/devtools/build/lib/packages/WorkspaceFactoryTest.java b/src/test/java/com/google/devtools/build/lib/packages/WorkspaceFactoryTest.java
index 8ad5c3c3466a7f..a345925d69857c 100644
--- a/src/test/java/com/google/devtools/build/lib/packages/WorkspaceFactoryTest.java
+++ b/src/test/java/com/google/devtools/build/lib/packages/WorkspaceFactoryTest.java
@@ -202,6 +202,7 @@ public void testImplicitMainRepoRename() throws Exception {
 
   @Test
   public void testNoImplicitMainRepoRenameWithoutFlag() throws Exception {
+    helper.setSkylarkSemantics("--noincompatible_remap_main_repo");
     helper.parse("workspace(name = 'foo')");
     RepositoryName foo = RepositoryName.create("@foo");
     assertThat(helper.getPackage().getRepositoryMapping(RepositoryName.create("@")))
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/RepositoryMappingFunctionTest.java b/src/test/java/com/google/devtools/build/lib/skyframe/RepositoryMappingFunctionTest.java
index 7da92b62b7fd82..b42d1012c9a23b 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/RepositoryMappingFunctionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/RepositoryMappingFunctionTest.java
@@ -66,7 +66,11 @@ public void testSimpleMapping() throws Exception {
         .hasEntryThat(skyKey)
         .isEqualTo(
             RepositoryMappingValue.withMapping(
-                ImmutableMap.of(RepositoryName.create("@a"), RepositoryName.create("@b"))));
+                ImmutableMap.of(
+                    RepositoryName.create("@a"),
+                    RepositoryName.create("@b"),
+                    RepositoryName.create("@good"),
+                    RepositoryName.create("@"))));
   }
 
   @Test
@@ -93,12 +97,20 @@ public void testMultipleRepositoriesWithMapping() throws Exception {
         .hasEntryThat(skyKey1)
         .isEqualTo(
             RepositoryMappingValue.withMapping(
-                ImmutableMap.of(RepositoryName.create("@a"), RepositoryName.create("@b"))));
+                ImmutableMap.of(
+                    RepositoryName.create("@a"),
+                    RepositoryName.create("@b"),
+                    RepositoryName.create("@good"),
+                    RepositoryName.create("@"))));
     assertThatEvaluationResult(eval(skyKey2))
         .hasEntryThat(skyKey2)
         .isEqualTo(
             RepositoryMappingValue.withMapping(
-                ImmutableMap.of(RepositoryName.create("@x"), RepositoryName.create("@y"))));
+                ImmutableMap.of(
+                    RepositoryName.create("@x"),
+                    RepositoryName.create("@y"),
+                    RepositoryName.create("@good"),
+                    RepositoryName.create("@"))));
   }
 
   @Test
@@ -119,8 +131,12 @@ public void testRepositoryWithMultipleMappings() throws Exception {
         .isEqualTo(
             RepositoryMappingValue.withMapping(
                 ImmutableMap.of(
-                    RepositoryName.create("@a"), RepositoryName.create("@b"),
-                    RepositoryName.create("@x"), RepositoryName.create("@y"))));
+                    RepositoryName.create("@a"),
+                    RepositoryName.create("@b"),
+                    RepositoryName.create("@x"),
+                    RepositoryName.create("@y"),
+                    RepositoryName.create("@good"),
+                    RepositoryName.create("@"))));
   }
 
   @Test
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/WorkspaceFileFunctionTest.java b/src/test/java/com/google/devtools/build/lib/skyframe/WorkspaceFileFunctionTest.java
index e6ef252d929d1c..f80fd99a3e9025 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/WorkspaceFileFunctionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/WorkspaceFileFunctionTest.java
@@ -299,17 +299,19 @@ public void testRepositoryMappingInChunks() throws Exception {
     RepositoryName b = RepositoryName.create("@b");
     RepositoryName x = RepositoryName.create("@x");
     RepositoryName y = RepositoryName.create("@y");
+    RepositoryName good = RepositoryName.create("@good");
+    RepositoryName main = RepositoryName.create("@");
 
     SkyKey key0 = WorkspaceFileValue.key(workspace, 0);
     EvaluationResult<WorkspaceFileValue> result0 = eval(key0);
     WorkspaceFileValue value0 = result0.get(key0);
-    assertThat(value0.getRepositoryMapping()).containsEntry(a, ImmutableMap.of(x, y));
+    assertThat(value0.getRepositoryMapping()).containsEntry(a, ImmutableMap.of(x, y, good, main));
 
     SkyKey key1 = WorkspaceFileValue.key(workspace, 1);
     EvaluationResult<WorkspaceFileValue> result1 = eval(key1);
     WorkspaceFileValue value1 = result1.get(key1);
-    assertThat(value1.getRepositoryMapping()).containsEntry(a, ImmutableMap.of(x, y));
-    assertThat(value1.getRepositoryMapping()).containsEntry(b, ImmutableMap.of(x, y));
+    assertThat(value1.getRepositoryMapping()).containsEntry(a, ImmutableMap.of(x, y, good, main));
+    assertThat(value1.getRepositoryMapping()).containsEntry(b, ImmutableMap.of(x, y, good, main));
   }
 
   @Test
diff --git a/src/test/shell/integration/starlark_configurations_external_workspaces_test.sh b/src/test/shell/integration/starlark_configurations_external_workspaces_test.sh
index dc4625fdc79c5d..52cb853cb03421 100755
--- a/src/test/shell/integration/starlark_configurations_external_workspaces_test.sh
+++ b/src/test/shell/integration/starlark_configurations_external_workspaces_test.sh
@@ -133,7 +133,7 @@ function test_set_flag_with_workspace_name() {
 
   write_build_setting_bzl "@${WORKSPACE_NAME}"
 
-  bazel build //$pkg:my_drink --@"${WORKSPACE_NAME}"//$pkg:type="coffee" \
+  bazel build //$pkg:my_drink --@//$pkg:type="coffee" \
     --experimental_build_setting_api > output 2>"$TEST_log" \
     || fail "Expected success"