diff --git a/src/libslic3r/GCode/WipeTowerEstimate.cpp b/src/libslic3r/GCode/WipeTowerEstimate.cpp
index 9b6c7882dd..e974f9351f 100644
--- a/src/libslic3r/GCode/WipeTowerEstimate.cpp
+++ b/src/libslic3r/GCode/WipeTowerEstimate.cpp
@@ -4,6 +4,7 @@
 #include "WipeTower.hpp"
 #include "WipeTower2.hpp"
 #include "../Config.hpp"
+#include "../FilamentMixer.hpp"
 #include "../PrintConfig.hpp"
 #include "../libslic3r.h"
 
@@ -74,10 +75,19 @@ Polygon estimate_wipe_tower_first_layer_outline(const ConfigBase &config, WipeTo
     return WipeTower2::cone_base_polygon(width, depth, height, cone ? cone_angle->getFloat() : 0.);
 }
 
-WipeTowerFootprint estimate_wipe_tower_footprint(const ConfigBase &config, WipeTowerType tower_type, const std::vector<unsigned int> &filament_ids, double layer_height, double max_object_height)
+WipeTowerFootprint estimate_wipe_tower_footprint(const ConfigBase &config, WipeTowerType tower_type, const std::vector<unsigned int> &filament_slots, double layer_height, double max_object_height)
 {
     WipeTowerFootprint footprint;
     footprint.height = max_object_height;
+    // A mixed slot is virtual: the tool ordering resolves it to one of its physical components
+    // on every layer, with or without colour sublayers, so the tower only ever purges those.
+    // Validation passes the slots as Print::extruders() lists them; the GUI and CLI placement
+    // expand them beforehand, which repeating here leaves unchanged.
+    std::vector<unsigned int> filament_ids = filament_slots;
+    const auto *is_mixed_opt   = dynamic_cast<const ConfigOptionBools *>(option_of(config, "filament_is_mixed"));
+    const auto *components_opt = dynamic_cast<const ConfigOptionStrings *>(option_of(config, "filament_mixed_components"));
+    if (is_mixed_opt != nullptr && components_opt != nullptr && has_any_mixed_filament(is_mixed_opt->values))
+        filament_ids = expand_mixed_filaments(filament_slots, is_mixed_opt->values, components_opt->values);
     const size_t filaments_cnt = filament_ids.size();
     if (filaments_cnt == 0 || layer_height < EPSILON)
         return footprint;
diff --git a/src/libslic3r/GCode/WipeTowerEstimate.hpp b/src/libslic3r/GCode/WipeTowerEstimate.hpp
index 1f0b674a11..9dad82f51f 100644
--- a/src/libslic3r/GCode/WipeTowerEstimate.hpp
+++ b/src/libslic3r/GCode/WipeTowerEstimate.hpp
@@ -34,6 +34,8 @@ Polygon estimate_wipe_tower_first_layer_outline(const ConfigBase &config, WipeTo
 // filament_ids:  0-based filaments purged on the plate. The config cannot see custom G-code tool
 //                changes, so ids derived from the model must include them
 //                (Print::extruders(true)) or a real tower is sized as if it were never built.
+//                A mixed slot may be passed as itself or already expanded: it is sized as its
+//                physical components either way, since those are all the tower ever purges.
 // layer_height:  thinnest layer the objects are sliced at. The first layer is folded in here.
 //
 // A raft is deliberately not a reason: normalize_fdm_2 clears enable_prime_tower for a plate
diff --git a/tests/libslic3r/test_wipe_tower_estimate.cpp b/tests/libslic3r/test_wipe_tower_estimate.cpp
index 6f520606a8..22117e686d 100644
--- a/tests/libslic3r/test_wipe_tower_estimate.cpp
+++ b/tests/libslic3r/test_wipe_tower_estimate.cpp
@@ -133,6 +133,28 @@ TEST_CASE("Type1 sizes the tower from each filament's own prime volume", "[WipeT
     CHECK_THAT(rib.depth, WithinAbs(WipeTower::estimate_rib_tower_bbox_side({{30.f, 0}, {45.f, 0}}, 35.f, 0.21f, 0.4f, 1.5f, 8.f, 0.f, 5.f), 1e-4));
 }
 
+TEST_CASE("A mixed slot is purged as its physical components", "[WipeTowerEstimate]") {
+    // Slots 4 and 5 blend 1+2 and 1+3: every layer prints one component per mixed slot, so a
+    // plate using all five slots purges the three physical filaments and nothing more.
+    const WipeTowerType type = GENERATE(WipeTowerType::Type1, WipeTowerType::Type2);
+    DynamicPrintConfig  config = make_config();
+    config.set_key_value("filament_prime_volume", new ConfigOptionFloats({100., 100., 100., 100., 100.}));
+    config.set_key_value("filament_adhesiveness_category", new ConfigOptionInts({0, 0, 0, 0, 0}));
+    config.set_key_value("filament_is_mixed", new ConfigOptionBools(std::vector<unsigned char>{0, 0, 0, 1, 1}));
+    config.set_key_value("filament_mixed_components", new ConfigOptionStrings({"", "", "", "1,2", "1,3"}));
+    const double physical = estimate(config, 3, 0.2, 5., type).depth;
+    REQUIRE(physical > estimate(config, 2, 0.2, 5., type).depth);
+    CHECK_THAT(estimate(config, 5, 0.2, 5., type).depth, WithinAbs(physical, 1e-9));
+    // The same slots with the mixed flags cleared are five filaments, which is what sized the
+    // tower before and refused positions the printed tower fits.
+    DynamicPrintConfig unmixed = config;
+    unmixed.set_key_value("filament_is_mixed", new ConfigOptionBools(std::vector<unsigned char>{0, 0, 0, 0, 0}));
+    CHECK(estimate(unmixed, 5, 0.2, 5., type).depth > physical);
+    // Mixed slots alone still purge their components, and a single one already changes tools.
+    CHECK_THAT(estimate_wipe_tower_footprint(config, type, {3, 4}, 0.2, 5.).depth, WithinAbs(physical, 1e-9));
+    CHECK_THAT(estimate_wipe_tower_footprint(config, type, {3}, 0.2, 5.).depth, WithinAbs(estimate(config, 2, 0.2, 5., type).depth, 1e-9));
+}
+
 TEST_CASE("A second nozzle adds the ramming of one nozzle change per layer", "[WipeTowerEstimate]") {
     // Two filaments on two nozzles: the tool order crosses once per layer, and Type1 rams 10 mm
     // of filament as three 1.0 mm nozzle-change lines (see the WipeTower case).