diff --git a/include/openPMD/IO/AbstractIOHandlerImplCommon.hpp b/include/openPMD/IO/AbstractIOHandlerImplCommon.hpp
index 7261b4bf71..4c995be817 100644
--- a/include/openPMD/IO/AbstractIOHandlerImplCommon.hpp
+++ b/include/openPMD/IO/AbstractIOHandlerImplCommon.hpp
@@ -28,10 +28,10 @@
 #include "openPMD/auxiliary/StringManip.hpp"
 #include "openPMD/backend/Writable.hpp"
 
+#include <set>
 #include <stdexcept>
 #include <string>
 #include <unordered_map>
-#include <unordered_set>
 
 namespace openPMD
 {
@@ -50,7 +50,10 @@ class AbstractIOHandlerImplCommon : public AbstractIOHandlerImpl
      * without the OS path
      */
     std::unordered_map<Writable *, InvalidatableFile> m_files;
-    std::unordered_set<InvalidatableFile> m_dirty;
+    // MUST be an ordered set in order to consistently flush on different
+    // parallel processes (same logic cant apply to m_files since Writable*
+    // pointers are not predictable)
+    std::set<InvalidatableFile> m_dirty;
 
     enum PossiblyExisting
     {
diff --git a/include/openPMD/IO/InvalidatableFile.hpp b/include/openPMD/IO/InvalidatableFile.hpp
index 6bdc24cbe6..6ac0051cbe 100644
--- a/include/openPMD/IO/InvalidatableFile.hpp
+++ b/include/openPMD/IO/InvalidatableFile.hpp
@@ -82,4 +82,14 @@ struct hash<openPMD::InvalidatableFile>
 
     result_type operator()(argument_type const &s) const noexcept;
 };
+
+template <>
+struct less<openPMD::InvalidatableFile>
+{
+    using first_argument_type = openPMD::InvalidatableFile;
+    using second_argument_type = first_argument_type;
+    using result_type = typename std::less<std::string>::result_type;
+    result_type
+    operator()(first_argument_type const &, second_argument_type const &) const;
+};
 } // namespace std
diff --git a/src/IO/ADIOS/ADIOS2IOHandler.cpp b/src/IO/ADIOS/ADIOS2IOHandler.cpp
index e9e5c7e53f..3f16bcf155 100644
--- a/src/IO/ADIOS/ADIOS2IOHandler.cpp
+++ b/src/IO/ADIOS/ADIOS2IOHandler.cpp
@@ -1747,7 +1747,7 @@ void ADIOS2IOHandlerImpl::listPaths(
      */
     auto &fileData = getFileData(file, IfFileNotOpen::ThrowError);
 
-    std::unordered_set<std::string> subdirs;
+    std::set<std::string> subdirs;
     /*
      * When reading an attribute, we cannot distinguish
      * whether its containing "folder" is a group or a
@@ -1889,7 +1889,7 @@ void ADIOS2IOHandlerImpl::listDatasets(
 
     auto &fileData = getFileData(file, IfFileNotOpen::ThrowError);
 
-    std::unordered_set<std::string> subdirs;
+    std::set<std::string> subdirs;
     for (auto var : fileData.availableVariablesPrefixed(myName))
     {
         // if string still contains a slash, variable is a dataset below the
diff --git a/src/IO/InvalidatableFile.cpp b/src/IO/InvalidatableFile.cpp
index cb6930da2b..c4a5d2c69f 100644
--- a/src/IO/InvalidatableFile.cpp
+++ b/src/IO/InvalidatableFile.cpp
@@ -80,3 +80,9 @@ std::hash<openPMD::InvalidatableFile>::operator()(
     return std::hash<shared_ptr<openPMD::InvalidatableFile::FileState>>{}(
         s.fileState);
 }
+auto std::less<openPMD::InvalidatableFile>::operator()(
+    first_argument_type const &first, second_argument_type const &second) const
+    -> result_type
+{
+    return less<>()(*first, *second);
+}