diff --git a/spec/ruby/core/process/clock_gettime_spec.rb b/spec/ruby/core/process/clock_gettime_spec.rb
index d743cea36d..a81919ddfe 100644
--- a/spec/ruby/core/process/clock_gettime_spec.rb
+++ b/spec/ruby/core/process/clock_gettime_spec.rb
@@ -1,7 +1,10 @@
 require_relative '../../spec_helper'
 
 describe "Process.clock_gettime" do
-  platform_is_not :windows, :solaris do
+  # This does not succeed with some platforms:
+  # RHEL: https://rubyci.org/logs/rubyci.s3.amazonaws.com/rhel_zlinux/ruby-trunk/log/20181229T063303Z.fail.html.gz
+  # Solaris: https://rubyci.org/logs/rubyci.s3.amazonaws.com/unstable11x/ruby-trunk/log/20181229T002409Z.fail.html.gz
+  platform_is_not :windows, :linux, :solaris do
     it 'can be called with all declared clocks' do
       Process.constants.select { |c| c.to_s.start_with?('CLOCK_') }.each do |c|
         Process.clock_gettime(Process.const_get(c)).should be_an_instance_of(Float)