diff --git a/src/OrcaSlicer.cpp b/src/OrcaSlicer.cpp
index 53f0352c09..7e1341ac18 100644
--- a/src/OrcaSlicer.cpp
+++ b/src/OrcaSlicer.cpp
@@ -1317,7 +1317,13 @@ int CLI::run(int argc, char **argv)
         return CLI_INVALID_PARAMS;
     }
     BOOST_LOG_TRIVIAL(info) << "finished setup params, argc="<< argc << std::endl;
-    std::string temp_path = wxFileName::GetTempDir().utf8_str().data();
+    std::string temp_path = per_user_temp_dir(wxFileName::GetTempDir().utf8_str().data(), per_user_temp_id());
+    // Some consumers write into the temp root directly, so create it up front.
+    try {
+        boost::filesystem::create_directories(temp_path);
+    } catch (const std::exception &ex) {
+        BOOST_LOG_TRIVIAL(warning) << "failed to create per-user temp dir " << temp_path << ": " << ex.what();
+    }
     set_temporary_dir(temp_path);
 
     m_extra_config.apply(m_config, true);
diff --git a/src/libslic3r/Utils.hpp b/src/libslic3r/Utils.hpp
index fee9f2e5ac..a76857dc4b 100644
--- a/src/libslic3r/Utils.hpp
+++ b/src/libslic3r/Utils.hpp
@@ -300,6 +300,10 @@ std::string header_gcodeviewer_generated();
 
 // getpid platform wrapper
 extern unsigned get_current_pid();
+// Per-user id for isolating temp dirs; empty on Windows (its temp dir is already per-user).
+std::string per_user_temp_id();
+// Per-user temp root under `base`; an empty `user_id` returns `base` unchanged.
+std::string per_user_temp_dir(const std::string &base, const std::string &user_id);
 // BBS: backup & restore
 std::string get_process_name(int pid);
 
diff --git a/src/libslic3r/utils.cpp b/src/libslic3r/utils.cpp
index f3edb516ab..131369d212 100644
--- a/src/libslic3r/utils.cpp
+++ b/src/libslic3r/utils.cpp
@@ -1285,6 +1285,24 @@ unsigned get_current_pid()
 #endif
 }
 
+std::string per_user_temp_id()
+{
+#ifdef WIN32
+    return {};
+#else
+    return std::to_string(static_cast<unsigned long>(::getuid()));
+#endif
+}
+
+std::string per_user_temp_dir(const std::string &base, const std::string &user_id)
+{
+    if (user_id.empty())
+        return base;
+    // Keep the id at the top level so each user's dir sits directly in the world-writable temp
+    // root; a shared parent dir would be owned by whichever user created it first.
+    return base + "/orcaslicer_" + user_id;
+}
+
 // BBS: backup & restore
 std::string get_process_name(int pid)
 {
diff --git a/tests/libslic3r/CMakeLists.txt b/tests/libslic3r/CMakeLists.txt
index d5e6eb958e..072e1a16b2 100644
--- a/tests/libslic3r/CMakeLists.txt
+++ b/tests/libslic3r/CMakeLists.txt
@@ -23,6 +23,7 @@ add_executable(${_TEST_NAME}_tests
     test_stl.cpp
     test_meshboolean.cpp
     test_marchingsquares.cpp
+    test_utils.cpp
     test_timeutils.cpp
     test_voronoi.cpp
     test_optimizers.cpp
diff --git a/tests/libslic3r/test_utils.cpp b/tests/libslic3r/test_utils.cpp
new file mode 100644
index 0000000000..c039069b2a
--- /dev/null
+++ b/tests/libslic3r/test_utils.cpp
@@ -0,0 +1,54 @@
+#include <catch2/catch_all.hpp>
+
+#include "libslic3r/Utils.hpp"
+
+#ifndef _WIN32
+#include <unistd.h>     // getuid
+#endif
+
+using namespace Slic3r;
+
+TEST_CASE("per_user_temp_dir composes a per-user temp root", "[utils]") {
+    const std::string base = "/tmp";
+
+    SECTION("an empty id returns base unchanged") {
+        REQUIRE(per_user_temp_dir(base, "") == base);
+    }
+    SECTION("a non-empty id is appended at the top level") {
+        REQUIRE(per_user_temp_dir(base, "1000") == base + "/orcaslicer_1000");
+    }
+    SECTION("distinct ids produce distinct roots") {
+        REQUIRE(per_user_temp_dir(base, "1000") != per_user_temp_dir(base, "1001"));
+    }
+}
+
+TEST_CASE("per_user_temp_id follows the platform contract", "[utils]") {
+    const std::string id = per_user_temp_id();
+
+    SECTION("stable across calls") {
+        REQUIRE(per_user_temp_id() == id);
+    }
+#ifdef _WIN32
+    SECTION("empty on Windows (its temp dir is already per-user)") {
+        REQUIRE(id.empty());
+    }
+#else
+    SECTION("the current uid on Linux/macOS") {
+        REQUIRE_FALSE(id.empty());
+        REQUIRE(id == std::to_string(static_cast<unsigned long>(::getuid())));
+    }
+#endif
+}
+
+// The end-to-end contract callers depend on: the temp root is left alone on
+// Windows and isolated per user on Linux/macOS.
+TEST_CASE("per-user temp root is unchanged on Windows, isolated elsewhere", "[utils]") {
+    const std::string base = "/tmp";
+    const std::string root = per_user_temp_dir(base, per_user_temp_id());
+#ifdef _WIN32
+    REQUIRE(root == base);
+#else
+    REQUIRE(root != base);
+    REQUIRE_THAT(root, Catch::Matchers::StartsWith(base + "/orcaslicer_"));
+#endif
+}