diff --git a/elasticgraph/spec/unit/elastic_graph/gem_spec.rb b/elasticgraph/spec/unit/elastic_graph/gem_spec.rb
index 6d31c76fe..5dc67b3ec 100644
--- a/elasticgraph/spec/unit/elastic_graph/gem_spec.rb
+++ b/elasticgraph/spec/unit/elastic_graph/gem_spec.rb
@@ -9,6 +9,7 @@
 require_relative "../../../../script/list_eg_gems"
 require "elastic_graph/support/json_schema/meta_schema_validator"
 require "elastic_graph/support/json_schema/validator"
+require "yaml"
 
 module ElasticGraph
   RSpec.describe "ElasticGraph gems" do
@@ -197,6 +198,24 @@ def with_load_paths(*paths)
       end
     end
 
+    # Every EG gem that ships RBS signatures (i.e. has a `sig` directory) must be listed in
+    # `rbs_collection.yaml` with `ignore: true`. Otherwise, `rbs collection install` pulls the
+    # gem's signatures in via bundler while those same signatures _also_ exist locally in this
+    # monorepo, and Steep fails with "declaration is duplicated" errors. The bootstrap gem
+    # `elasticgraph` (no dash) ships no signatures, so it is intentionally excluded.
+    it "ignores every EG gem that ships RBS signatures in `rbs_collection.yaml` to avoid Steep `declaration is duplicated` errors" do
+      eg_gems_with_sig = ::ElasticGraphGems.list.select do |gem_name|
+        ::File.directory?(::File.join(CommonSpecHelpers::REPO_ROOT, gem_name, "sig"))
+      end
+
+      rbs_config = ::YAML.safe_load_file(::File.join(CommonSpecHelpers::REPO_ROOT, "rbs_collection.yaml"))
+      ignored_eg_gems = rbs_config.fetch("gems")
+        .select { |gem| gem.fetch("name").start_with?("elasticgraph") && gem["ignore"] == true }
+        .map { |gem| gem.fetch("name") }
+
+      expect(ignored_eg_gems).to match_array(eg_gems_with_sig)
+    end
+
     # We don't expect any variation in these gemspec attributes.
     %i[homepage license required_ruby_version version].each do |gemspec_attribute|
       it "has the same value for `#{gemspec_attribute}` in all ElasticGraph gemspecs" do
diff --git a/rbs_collection.yaml b/rbs_collection.yaml
index e6db4655f..e19fbb28d 100644
--- a/rbs_collection.yaml
+++ b/rbs_collection.yaml
@@ -74,6 +74,8 @@ gems:
     ignore: true
   - name: elasticgraph-indexer_lambda
     ignore: true
+  - name: elasticgraph-json_ingestion
+    ignore: true
   - name: elasticgraph-lambda_support
     ignore: true
   - name: elasticgraph-local