diff --git a/lib/bundler/yaml_serializer.rb b/lib/bundler/yaml_serializer.rb
index 93d08a05aa..ab1eb6dbcf 100644
--- a/lib/bundler/yaml_serializer.rb
+++ b/lib/bundler/yaml_serializer.rb
@@ -41,7 +41,7 @@ module Bundler
     HASH_REGEX = /
       ^
       ([ ]*) # indentations
-      (.+) # key
+      ([^#]+) # key excludes comment char '#'
       (?::(?=(?:\s|$))) # :  (without the lookahead the #key includes this when : is present in value)
       [ ]?
       (['"]?) # optional opening quote
diff --git a/lib/rubygems/yaml_serializer.rb b/lib/rubygems/yaml_serializer.rb
index af86c63ef7..f89004f32a 100644
--- a/lib/rubygems/yaml_serializer.rb
+++ b/lib/rubygems/yaml_serializer.rb
@@ -41,7 +41,7 @@ module Gem
     HASH_REGEX = /
       ^
       ([ ]*) # indentations
-      (.+) # key
+      ([^#]+) # key excludes comment char '#'
       (?::(?=(?:\s|$))) # :  (without the lookahead the #key includes this when : is present in value)
       [ ]?
       (['"]?) # optional opening quote
diff --git a/test/rubygems/test_gem_config_file.rb b/test/rubygems/test_gem_config_file.rb
index b28dcf503e..4230eda4d3 100644
--- a/test/rubygems/test_gem_config_file.rb
+++ b/test/rubygems/test_gem_config_file.rb
@@ -569,10 +569,14 @@ if you believe they were disclosed to a third party.
     yaml = <<~YAML
       ---
       :foo: bar # buzz
+      #:notkey: bar
     YAML
 
     actual = Gem::ConfigFile.load_with_rubygems_config_hash(yaml)
     assert_equal("bar", actual[:foo])
+    assert_equal(false, actual.key?("#:notkey"))
+    assert_equal(false, actual.key?(:notkey))
+    assert_equal(1, actual.size)
   end
 
   def test_s3_source