diff --git a/Library/Homebrew/dev-cmd/tests.rb b/Library/Homebrew/dev-cmd/tests.rb
index ec512f72cb..e19945baac 100644
--- a/Library/Homebrew/dev-cmd/tests.rb
+++ b/Library/Homebrew/dev-cmd/tests.rb
@@ -3,6 +3,7 @@
 
 require "abstract_command"
 require "fileutils"
+require "hardware"
 require "system_command"
 
 module Homebrew
@@ -75,7 +76,13 @@ module Homebrew
             end
           end
 
-          parallel = false if args.profile
+          # We use `ParallelTests.last_process?` in `test/spec_helper.rb` to
+          # handle SimpleCov output but, due to how the method is implemented,
+          # it doesn't work as expected if the number of processes is greater
+          # than one but lower than the number of CPU cores in the execution
+          # environment. Coverage information isn't saved in that scenario,
+          # so we disable parallel testing as a workaround in this case.
+          parallel = false if args.profile || (args.coverage? && files.length < Hardware::CPU.cores)
 
           parallel_rspec_log_name = "parallel_runtime_rspec"
           parallel_rspec_log_name = "#{parallel_rspec_log_name}.generic" if args.generic?