diff --git a/WORKSPACE b/WORKSPACE
index 23c896a..eb010a4 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -15,7 +15,7 @@ rules_swc_dependencies()
 load("//swc:repositories.bzl", "swc_register_toolchains")
 
 swc_register_toolchains(
-    name = "swc",
+    name = "default_swc",
     swc_version = "v1.2.119",
 )
 
diff --git a/examples/macro/ts_project.bzl b/examples/macro/ts_project.bzl
index 000e848..865514c 100644
--- a/examples/macro/ts_project.bzl
+++ b/examples/macro/ts_project.bzl
@@ -23,9 +23,9 @@ def my_ts_project(name, srcs = []):
                 $(execpath @aspect_rules_swc//swc:cli) \\
                 $(location in.ts) \\
                 -o $@""",
-            toolchains = ["@swc_toolchains//:resolved_toolchain"],
+            toolchains = ["@default_swc_toolchains//:resolved_toolchain"],
             tools = [
                 "@aspect_rules_swc//swc:cli",
-                "@swc_toolchains//:resolved_toolchain",
+                "@default_swc_toolchains//:resolved_toolchain",
             ],
         )
diff --git a/swc/BUILD.bazel b/swc/BUILD.bazel
index 9ca4fd4..df8cbed 100644
--- a/swc/BUILD.bazel
+++ b/swc/BUILD.bazel
@@ -35,8 +35,12 @@ write_file(
 nodejs_binary(
     name = "cli",
     data = [
-        "@npm__swc_cli-0.1.52",
-        "@npm__swc_core-1.2.119",
+        # Don't use the shorter syntax here because the user or bzlmod
+        # might use repository mapping to give a different name
+        # to the repository, e.g.
+        # @aspect_rules_swc.0.2.0.swc.npm__swc_core-1.2.119
+        "@npm__swc_cli-0.1.52//:pkg",
+        "@npm__swc_core-1.2.119//:pkg",
     ],
     entry_point = "main.js",
     visibility = ["//visibility:public"],
diff --git a/swc/dependencies.bzl b/swc/dependencies.bzl
index f27394b..73ae9b8 100644
--- a/swc/dependencies.bzl
+++ b/swc/dependencies.bzl
@@ -41,7 +41,7 @@ def rules_swc_dependencies():
     maybe(
         http_archive,
         name = "aspect_rules_js",
-        sha256 = "e8576a74a7e80b873179514cf1ad48b62b18ae024e74200ecd40ae6dc00c515a",
-        strip_prefix = "rules_js-0.3.0",
-        url = "https://github.com/aspect-build/rules_js/archive/v0.3.0.tar.gz",
+        sha256 = "dd78b4911b7c2e6c6e919b85cd31572cc15e5baa62b9e7354d8a1065c67136e3",
+        strip_prefix = "rules_js-0.3.1",
+        url = "https://github.com/aspect-build/rules_js/archive/v0.3.1.tar.gz",
     )
diff --git a/swc/extensions.bzl b/swc/extensions.bzl
new file mode 100644
index 0000000..d6db15d
--- /dev/null
+++ b/swc/extensions.bzl
@@ -0,0 +1,35 @@
+"extensions for bzlmod"
+
+load(":repositories.bzl", "swc_register_toolchains")
+
+swc_toolchain = tag_class(attrs = {
+    "name": attr.string(doc = "Base name for generated repositories"),
+    "swc_version": attr.string(doc = "Version of the swc rust binding"),
+})
+
+def _toolchain_extension(module_ctx):
+    registrations = {}
+    for mod in module_ctx.modules:
+        for toolchain in mod.tags.toolchain:
+            if toolchain.name in registrations.keys():
+                if toolchain.swc_version == registrations[toolchain.name]:
+                    # No problem to register a matching toolchain twice
+                    continue
+                fail("Multiple conflicting toolchains declared for name {} ({} and {}".format(
+                    toolchain.name,
+                    toolchain.swc_version,
+                    registrations[toolchain.name],
+                ))
+            else:
+                registrations[toolchain.name] = toolchain.swc_version
+    for name, swc_version in registrations.items():
+        swc_register_toolchains(
+            name = name,
+            swc_version = swc_version,
+            register = False,
+        )
+
+swc = module_extension(
+    implementation = _toolchain_extension,
+    tag_classes = {"toolchain": swc_toolchain},
+)
diff --git a/swc/repositories.bzl b/swc/repositories.bzl
index ab0c1cc..4e2acb8 100644
--- a/swc/repositories.bzl
+++ b/swc/repositories.bzl
@@ -41,7 +41,7 @@ swc_repositories = repository_rule(
 )
 
 # Wrapper macro around everything above, this is the primary API
-def swc_register_toolchains(name, **kwargs):
+def swc_register_toolchains(name, register = True, **kwargs):
     """Convenience macro for users which does typical setup.
 
     - create a repository for each built-in platform like "swc_linux_amd64" -
@@ -52,6 +52,8 @@ def swc_register_toolchains(name, **kwargs):
     Users can avoid this macro and do these steps themselves, if they want more control.
     Args:
         name: base name for all created repos, like "swc"
+        register: whether to call through to native.register_toolchains.
+            Should be True for WORKSPACE users, but false when used under bzlmod extension
         **kwargs: passed to each node_repositories call
     """
     for platform in PLATFORMS.keys():
@@ -60,7 +62,8 @@ def swc_register_toolchains(name, **kwargs):
             platform = platform,
             **kwargs
         )
-        native.register_toolchains("@%s_toolchains//:%s_toolchain" % (name, platform))
+        if register:
+            native.register_toolchains("@%s_toolchains//:%s_toolchain" % (name, platform))
 
     toolchains_repo(
         name = name + "_toolchains",