diff --git a/src/libslic3r/GCode/WipeTowerEstimate.cpp b/src/libslic3r/GCode/WipeTowerEstimate.cpp
index 6fee774e9c..f40f2899fd 100644
--- a/src/libslic3r/GCode/WipeTowerEstimate.cpp
+++ b/src/libslic3r/GCode/WipeTowerEstimate.cpp
@@ -96,12 +96,9 @@ WipeTowerFootprint estimate_wipe_tower_footprint(const ConfigBase &config, WipeT
     // normalize_fdm_2 clearing enable_prime_tower. Its mixed-filament case is not modelled.
     const bool   need_wipe_tower  = smooth_timelapse || wrapping;
 
-    // No tool change, nothing to purge; smooth timelapse still primes once.
-    size_t purge_count = 0;
-    if (filaments_cnt > 1)
-        purge_count = dual_nozzle ? filaments_cnt : filaments_cnt - 1;
-    else if (smooth_timelapse)
-        purge_count = 1;
+    // A tower printed for one of the reasons above has no tool change to purge for; both
+    // planners give it the idle depth below and nothing more.
+    const size_t purge_count = filaments_cnt > 1 ? (dual_nozzle ? filaments_cnt : filaments_cnt - 1) : 0;
 
     // Type2 purges one volume per tool change. Type1 plans per filament below; here the volume
     // only decides whether a tower exists.
diff --git a/src/slic3r/GUI/PartPlate.cpp b/src/slic3r/GUI/PartPlate.cpp
index bf511ec657..e73d43b782 100644
--- a/src/slic3r/GUI/PartPlate.cpp
+++ b/src/slic3r/GUI/PartPlate.cpp
@@ -2341,10 +2341,12 @@ WipeTowerFootprint PartPlate::estimate_wipe_tower_footprint(const DynamicPrintCo
         if (std::find(plate_extruders.begin(), plate_extruders.end(), id) == plate_extruders.end())
             plate_extruders.push_back(id);
     // The wipe tower filament joins the tool ordering even when unused (Print::extruders), so
-    // validation counts it.
+    // validation counts it - but only where there is a tower to join, which is the
+    // has_wipe_tower() half of that guard.
     const ConfigOption *wipe_tower_filament_opt = config.option("wipe_tower_filament");
+    const ConfigOption *enable_prime_tower_opt  = config.option("enable_prime_tower");
     const int           wipe_tower_filament     = wipe_tower_filament_opt != nullptr ? wipe_tower_filament_opt->getInt() : 0;
-    if (plate_extruders.size() > 1 && wipe_tower_filament > 0 &&
+    if (enable_prime_tower_opt != nullptr && enable_prime_tower_opt->getBool() && plate_extruders.size() > 1 && wipe_tower_filament > 0 &&
         std::find(plate_extruders.begin(), plate_extruders.end(), wipe_tower_filament) == plate_extruders.end())
         plate_extruders.push_back(wipe_tower_filament);
     if (plate_extruders.empty())
diff --git a/tests/libslic3r/test_wipe_tower_estimate.cpp b/tests/libslic3r/test_wipe_tower_estimate.cpp
index ae0a92f40a..fee5c1f152 100644
--- a/tests/libslic3r/test_wipe_tower_estimate.cpp
+++ b/tests/libslic3r/test_wipe_tower_estimate.cpp
@@ -171,22 +171,28 @@ TEST_CASE("A single filament only gets a tower when one is printed anyway", "[Wi
     config.set_key_value("raft_layers", new ConfigOptionInt(0));
 
     config.set_deserialize_strict("timelapse_type", "1");
-    // Smooth timelapse primes the single filament once: 10 mm, lifted to the floor.
+    // A tower printed with no tool change is exactly the planner's idle depth: there is
+    // nothing to purge, and WipeTower2 sizes it at the stability floor.
     CHECK_THAT(estimate(config, 1, 0.2, 100.).depth, WithinAbs(20., 1e-9));
-    CHECK_THAT(estimate(config, 1, 0.2, 5.).depth, WithinAbs(10., 1e-9));
+    CHECK_THAT(estimate(config, 1, 0.2, 5.).depth, WithinAbs(WipeTower::get_limit_depth_by_height(5.f), 1e-9));
 }
 
-TEST_CASE("A tool change reserves the stability floor even with nothing to purge", "[WipeTowerEstimate]") {
-    // The purge volumes are configurable down to zero, but the tool changes are still printed on
-    // the tower and the generator still floors it, so the estimate has to floor it too.
-    const double       height = GENERATE(5., 100.);
-    const float        floor  = WipeTower::get_limit_depth_by_height(float(height));
-    DynamicPrintConfig config = make_config(GENERATE("rectangle", "rib"));
+TEST_CASE("A tool change reserves a tower even with nothing to purge", "[WipeTowerEstimate]") {
+    // The purge volumes are configurable down to zero, but the tool changes are still printed
+    // on the tower and both planners still floor it - so the estimate has to floor it too.
+    // Type1 plans per filament and already reserves one; Type2 has only the volume to go on.
+    const double     height = GENERATE(5., 100.);
+    const float      floor  = WipeTower::get_limit_depth_by_height(float(height));
+    const char      *wall   = GENERATE("rectangle", "rib");
+    DynamicPrintConfig config = make_config(wall);
     config.set_key_value("prime_volume", new ConfigOptionFloat(0.));
+    config.set_key_value("filament_prime_volume", new ConfigOptionFloats({0.}));
 
-    CHECK(estimate(config, 3, 0.2, height).depth >= floor);
+    CHECK(estimate(config, 3, 0.2, height, WipeTowerType::Type2).depth >= floor);
+    CHECK(estimate(config, 3, 0.2, height, WipeTowerType::Type1).depth >= floor);
     // Still nothing for a lone filament with no other reason.
-    CHECK_THAT(estimate(config, 1, 0.2, height).depth, WithinAbs(0., 1e-9));
+    CHECK_THAT(estimate(config, 1, 0.2, height, WipeTowerType::Type2).depth, WithinAbs(0., 1e-9));
+    CHECK_THAT(estimate(config, 1, 0.2, height, WipeTowerType::Type1).depth, WithinAbs(0., 1e-9));
 }
 
 TEST_CASE("Both wall types agree on whether there is a tower at all", "[WipeTowerEstimate]") {