diff --git a/lib/slather/coverage_info.rb b/lib/slather/coverage_info.rb
index 1fad52b..85c963f 100644
--- a/lib/slather/coverage_info.rb
+++ b/lib/slather/coverage_info.rb
@@ -71,7 +71,15 @@ def rate_branches_tested
     end
 
     def source_file_pathname_relative_to_repo_root
-      source_file_pathname.realpath.relative_path_from(Pathname("./").realpath)
+      test_path=source_file_pathname
+      equivalence=ENV["COVERAGE_PATH_EQUIVALENCE"]
+      if equivalence
+        orig_prefix=equivalence.delete_suffix(",.")
+        if "#{source_file_pathname}".start_with?(orig_prefix)
+          test_path=Pathname("." + "#{source_file_pathname}".delete_prefix(orig_prefix))
+        end
+      end
+      test_path.realpath.relative_path_from(Pathname("./").realpath)
     end
 
     def ignored?
diff --git a/lib/slather/project.rb b/lib/slather/project.rb
index 2253431..82385d0 100755
--- a/lib/slather/project.rb
+++ b/lib/slather/project.rb
@@ -269,6 +269,9 @@ def unsafe_llvm_cov_export_output(binary_path)
       if self.arch
         llvm_cov_args << "--arch" << self.arch
       end
+      if ENV["COVERAGE_PATH_EQUIVALENCE"]
+        llvm_cov_args << "-path-equivalence=#{ENV["COVERAGE_PATH_EQUIVALENCE"]}"
+      end
       `xcrun llvm-cov #{llvm_cov_args.shelljoin}`
     end
     private :unsafe_llvm_cov_export_output
@@ -293,6 +296,9 @@ def unsafe_profdata_llvm_cov_output(binary_path, source_files)
       if self.arch
         llvm_cov_args << "--arch" << self.arch
       end
+      if ENV["COVERAGE_PATH_EQUIVALENCE"]
+        llvm_cov_args << "-path-equivalence=#{ENV["COVERAGE_PATH_EQUIVALENCE"]}"
+      end
 
       # POSIX systems have an ARG_MAX for the maximum total length of the command line, so the command may fail with an error message of "Argument list too long".
       # Using the xargs command we can break the list of source_files into sublists small enough to be acceptable.