diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 0f398f29c..cd8732829 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -21,9 +21,9 @@ jobs:
   test:
     strategy:
       matrix:
-        os: [ubuntu-latest, windows-latest]
+        os: ['ubuntu-20.04', windows-latest]
         ruby:
-          - 2.0
+          - '2.0'
           - 2.1
           - 2.2
           - 2.3
diff --git a/spec/pry_spec.rb b/spec/pry_spec.rb
index 892b437df..471da6f90 100644
--- a/spec/pry_spec.rb
+++ b/spec/pry_spec.rb
@@ -194,10 +194,6 @@ class Hello
             skip "jruby allows mutex usage in signal handlers"
           end
 
-          if Gem::Version.new(RUBY_VERSION) < Gem::Version.new("2.0.0")
-            skip "pre-2.0 mri allows mutex usage in signal handlers"
-          end
-
           trap("USR1") { @str_output = mock_pry }
         end
 
@@ -210,6 +206,9 @@ class Hello
         it "should return with error message" do
           expect(mock_pry('1 + 1')).to eql("=> 2\n")
           Process.kill("USR1", Process.pid)
+
+          sleep 0.01 if Gem::Version.new(RUBY_VERSION) < Gem::Version.new("2.1.0")
+
           expect(@str_output).to match(/Unable to obtain mutex lock/)
         end
       end