diff --git a/defs/gmake.mk b/defs/gmake.mk
index 0320f9b7d553fb..a05f5943aa981a 100644
--- a/defs/gmake.mk
+++ b/defs/gmake.mk
@@ -358,6 +358,21 @@ $(srcdir)/gems/%.gem:
 extract-gems: | $(patsubst %,$(srcdir)/.bundle/gems/%,$(bundled-gems))
 extract-gems: | $(call foreach-bundled-gems-rev,bundled-gem-extracted)
 
+# Docs targets call $(RDOC) -> tool/rdoc-srcdir, which loads rdoc/rdoc and
+# activates its `add_dependency 'rbs', '>= 4.0.0'`. Activation requires
+# the bundled rbs gem to be discoverable and its C extension built. The
+# existing per-bundled-gem Makefile generated by ext/extmk.rb does both
+# (extension build + copy of .bundled.rbs-*.gemspec into
+# .bundle/specifications/), but only if ext/configure-ext.mk has seen
+# `.bundle/gems/` populated when its template's
+# `Dir.glob(".bundle/gems/**/extconf.rb")` runs. On a clean tree
+# prepare-gems may not have run yet, so make the dep explicit for the
+# docs goals. Other targets are left alone so a plain `make` doesn't
+# reach for prepare-gems -> update-gems (network).
+ifneq ($(filter rdoc rdoc:% html html-server rdoc-coverage undocumented docs install install-all install-doc install-html install-rdoc reinstall,$(MAKECMDGOALS)),)
+ext/configure-ext.mk: $(HAVE_BASERUBY:yes=prepare-gems)
+endif
+
 $(srcdir)/.bundle/gems/%: $(srcdir)/gems/%.gem | .bundle/gems
 	$(ECHO) Extracting bundle gem $*...
 	$(Q) $(BASERUBY) -C "$(srcdir)" \
diff --git a/tool/update-deps b/tool/update-deps
index 2d4a5674be72a7..bfaf1fe0989aaa 100755
--- a/tool/update-deps
+++ b/tool/update-deps
@@ -328,12 +328,13 @@ def read_make_deps(cwd)
       next if /libyjit.o\z/ =~ target.to_s # skip YJIT Rust object (no corresponding C source)
       next if /libzjit.o\z/ =~ target.to_s # skip ZJIT Rust object (no corresponding C source)
       next if /target\/release\/libruby.o\z/ =~ target.to_s # skip YJIT+ZJIT Rust object (no corresponding C source)
-      next if /\.bundle\// =~ target.to_s
       next if /\A\./ =~ target.to_s # skip rules such as ".c.o"
       #p [curdir, target, deps]
       dir = curdir || dirstack.last
-      dependencies[dir + target] ||= []
-      dependencies[dir + target] |= deps.map {|dep| dir + dep }
+      key = dir + target
+      next if /\.bundle\// =~ key.to_s # bundled gem extensions manage their own depend files
+      dependencies[key] ||= []
+      dependencies[key] |= deps.map {|dep| dir + dep }
     elsif data_base_end
       curdir = nil
     elsif directory_leave