diff --git a/src/libslic3r/PresetBundle.cpp b/src/libslic3r/PresetBundle.cpp
index ae8aec1bd3..7ec2b59ca0 100644
--- a/src/libslic3r/PresetBundle.cpp
+++ b/src/libslic3r/PresetBundle.cpp
@@ -5381,13 +5381,15 @@ void PresetBundle::load_config_file_config(const std::string &name_or_path, bool
     bool process_multi_extruder = false;
     std::vector<int> filament_variant_index;
     size_t extruder_variant_count;
-    if (!config.option<ConfigOptionInts>("filament_self_index")) {
-        std::vector<int>& filament_self_indice = config.option<ConfigOptionInts>("filament_self_index", true)->values;
+    // A config loaded over the full defaults has a one-entry index even when the file has none.
+    ConfigOptionInts* filament_self_index_opt = config.option<ConfigOptionInts>("filament_self_index", true);
+    if (filament_self_index_opt->size() < num_filaments) {
+        std::vector<int>& filament_self_indice = filament_self_index_opt->values;
         filament_self_indice.resize(num_filaments);
         for (int index = 0; index < num_filaments; index++)
             filament_self_indice[index] = index + 1;
     }
-    std::vector<int> filament_self_indice = std::move(config.option<ConfigOptionInts>("filament_self_index")->values);
+    std::vector<int> filament_self_indice = std::move(filament_self_index_opt->values);
     // ORCA: Initialize filament_extruder_variant for backward compatibility with old 3mf files
     // that don't have this option saved or have it with default single-element value
     ConfigOptionStrings* filament_extruder_variant_opt = config.option<ConfigOptionStrings>("filament_extruder_variant");
diff --git a/tests/libslic3r/test_preset_bundle_loading.cpp b/tests/libslic3r/test_preset_bundle_loading.cpp
index e1ae29b473..50d368763d 100644
--- a/tests/libslic3r/test_preset_bundle_loading.cpp
+++ b/tests/libslic3r/test_preset_bundle_loading.cpp
@@ -5888,6 +5888,21 @@ TEST_CASE("A project saved with pressure advance per filament applies it to ever
     check_double_vector(petg.opt<ConfigOptionFloatsNullable>("filament_flow_ratio")->values, { 0.97 });
 }
 
+TEST_CASE("A multi-toolhead project saved without filament self indices loads every filament", "[Preset][Bundle]")
+{
+    const std::vector<std::string> colors = { "#FF0000", "#000000", "#FFFFFF", "#FFFF00" };
+    DynamicPrintConfig config = DynamicPrintConfig::full_print_config();
+    config.opt<ConfigOptionStrings>("filament_colour")->values = colors;
+    config.opt<ConfigOptionFloats>("nozzle_diameter")->values = std::vector<double>(colors.size(), 0.4);
+    config.option<ConfigOptionBool>("single_extruder_multi_material")->value = false;
+    Preset::normalize(config);
+
+    PresetBundle bundle;
+    REQUIRE_NOTHROW(bundle.load_config_model("test.3mf", std::move(config)));
+    CHECK(bundle.filament_presets.size() == colors.size());
+    CHECK(bundle.project_config.opt<ConfigOptionStrings>("filament_colour")->values == colors);
+}
+
 TEST_CASE("A system preset resolves by name from the bundled profiles", "[Preset][Bundle]")
 {
     ScopedTemporaryDir temp_dir;