diff --git a/BUILD b/BUILD
index d9d5a0c266..3dfb7a4eea 100644
--- a/BUILD
+++ b/BUILD
@@ -46,7 +46,7 @@ load(
 
 # begin:github_only
 load(
-    "//bazel:build_defs.bzl",
+    "//bazel:amalgamation.bzl",
     "upb_amalgamation",
 )
 # end:github_only
diff --git a/bazel/amalgamation.bzl b/bazel/amalgamation.bzl
new file mode 100644
index 0000000000..cabbaccd91
--- /dev/null
+++ b/bazel/amalgamation.bzl
@@ -0,0 +1,85 @@
+# Copyright (c) 2009-2021, Google LLC
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#     * Redistributions of source code must retain the above copyright
+#       notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above copyright
+#       notice, this list of conditions and the following disclaimer in the
+#       documentation and/or other materials provided with the distribution.
+#     * Neither the name of Google LLC nor the
+#       names of its contributors may be used to endorse or promote products
+#       derived from this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED. IN NO EVENT SHALL Google LLC BE LIABLE FOR ANY
+# DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""Internal rules for building upb."""
+
+load(":upb_proto_library.bzl", "GeneratedSrcsInfo")
+
+# upb_amalgamation() rule, with file_list aspect.
+
+SrcList = provider(
+    fields = {
+        "srcs": "list of srcs",
+    },
+)
+
+def _file_list_aspect_impl(target, ctx):
+    if GeneratedSrcsInfo in target:
+        srcs = target[GeneratedSrcsInfo]
+        return [SrcList(srcs = srcs.srcs + srcs.hdrs)]
+
+    srcs = []
+    for src in ctx.rule.attr.srcs:
+        srcs += src.files.to_list()
+    for hdr in ctx.rule.attr.hdrs:
+        srcs += hdr.files.to_list()
+    for hdr in ctx.rule.attr.textual_hdrs:
+        srcs += hdr.files.to_list()
+    return [SrcList(srcs = srcs)]
+
+_file_list_aspect = aspect(
+    implementation = _file_list_aspect_impl,
+)
+
+def _upb_amalgamation(ctx):
+    inputs = []
+    for lib in ctx.attr.libs:
+        inputs += lib[SrcList].srcs
+    srcs = [src for src in inputs if not src.path.endswith("hpp")]
+    ctx.actions.run(
+        inputs = inputs,
+        outputs = ctx.outputs.outs,
+        arguments = [f.path for f in ctx.outputs.outs] + [f.path for f in srcs],
+        progress_message = "Making amalgamation",
+        executable = ctx.executable._amalgamator,
+    )
+    return []
+
+upb_amalgamation = rule(
+    attrs = {
+        "_amalgamator": attr.label(
+            executable = True,
+            cfg = "exec",
+            default = "//bazel:amalgamate",
+        ),
+        "prefix": attr.string(
+            default = "",
+        ),
+        "libs": attr.label_list(aspects = [_file_list_aspect]),
+        "outs": attr.output_list(),
+        "strip_import_prefix": attr.string_list(),
+    },
+    implementation = _upb_amalgamation,
+)
diff --git a/bazel/build_defs.bzl b/bazel/build_defs.bzl
index 15be25c97e..e4212b3c67 100644
--- a/bazel/build_defs.bzl
+++ b/bazel/build_defs.bzl
@@ -25,8 +25,6 @@
 
 """Internal rules for building upb."""
 
-load(":upb_proto_library.bzl", "GeneratedSrcsInfo")
-
 _DEFAULT_CPPOPTS = []
 _DEFAULT_COPTS = []
 
@@ -101,60 +99,3 @@ def make_shell_script(name, contents, out):
         outs = [out],
         cmd = "(cat <<'HEREDOC'\n%s\nHEREDOC\n) > $@" % contents,
     )
-
-# upb_amalgamation() rule, with file_list aspect.
-
-SrcList = provider(
-    fields = {
-        "srcs": "list of srcs",
-    },
-)
-
-def _file_list_aspect_impl(target, ctx):
-    if GeneratedSrcsInfo in target:
-        srcs = target[GeneratedSrcsInfo]
-        return [SrcList(srcs = srcs.srcs + srcs.hdrs)]
-
-    srcs = []
-    for src in ctx.rule.attr.srcs:
-        srcs += src.files.to_list()
-    for hdr in ctx.rule.attr.hdrs:
-        srcs += hdr.files.to_list()
-    for hdr in ctx.rule.attr.textual_hdrs:
-        srcs += hdr.files.to_list()
-    return [SrcList(srcs = srcs)]
-
-_file_list_aspect = aspect(
-    implementation = _file_list_aspect_impl,
-)
-
-def _upb_amalgamation(ctx):
-    inputs = []
-    for lib in ctx.attr.libs:
-        inputs += lib[SrcList].srcs
-    srcs = [src for src in inputs if not src.path.endswith("hpp")]
-    ctx.actions.run(
-        inputs = inputs,
-        outputs = ctx.outputs.outs,
-        arguments = [f.path for f in ctx.outputs.outs] + [f.path for f in srcs],
-        progress_message = "Making amalgamation",
-        executable = ctx.executable._amalgamator,
-    )
-    return []
-
-upb_amalgamation = rule(
-    attrs = {
-        "_amalgamator": attr.label(
-            executable = True,
-            cfg = "exec",
-            default = "//bazel:amalgamate",
-        ),
-        "prefix": attr.string(
-            default = "",
-        ),
-        "libs": attr.label_list(aspects = [_file_list_aspect]),
-        "outs": attr.output_list(),
-        "strip_import_prefix": attr.string_list(),
-    },
-    implementation = _upb_amalgamation,
-)