diff --git a/tests/fff_print/test_helpers.cpp b/tests/fff_print/test_helpers.cpp
index 89f9f9fdd1..585132bc6e 100644
--- a/tests/fff_print/test_helpers.cpp
+++ b/tests/fff_print/test_helpers.cpp
@@ -224,6 +224,19 @@ DynamicPrintConfig multifilament_config(unsigned int filaments, std::initializer
 	return config;
 }
 
+void size_flush_to_nozzles(DynamicPrintConfig &config)
+{
+	// One filaments x filaments flush block and one flush multiplier per nozzle, as the GUI
+	// sizes them when the nozzle count changes; a single block leaves each nozzle's slice short.
+	const size_t nozzles = config.option<ConfigOptionFloats>("nozzle_diameter")->values.size();
+	auto        &flush   = config.option<ConfigOptionFloats>("flush_volumes_matrix", true)->values;
+	const std::vector<double> block = flush;
+	for (size_t i = 1; i < nozzles; ++i)
+		flush.insert(flush.end(), block.begin(), block.end());
+	for (const char *key : { "flush_multiplier", "flush_multiplier_fast" })
+		config.option<ConfigOptionFloats>(key, true)->resize(nozzles);
+}
+
 void init_print(std::vector<TriangleMesh> &&meshes, Slic3r::Print &print, Slic3r::Model &model, const DynamicPrintConfig &config_in,
                 const std::vector<std::vector<ConfigBase::SetDeserializeItem>> *per_object_overrides, bool arrange, size_t instances)
 {
diff --git a/tests/fff_print/test_helpers.hpp b/tests/fff_print/test_helpers.hpp
index cbdc90c3d9..1dee775092 100644
--- a/tests/fff_print/test_helpers.hpp
+++ b/tests/fff_print/test_helpers.hpp
@@ -72,6 +72,10 @@ Slic3r::Model model(const std::string& model_name, TriangleMesh&& _mesh);
 DynamicPrintConfig multifilament_config(unsigned int filaments,
     std::initializer_list<Slic3r::ConfigBase::SetDeserializeItem> extra = {});
 
+// Repeat multifilament_config's single flush block, and the flush multipliers, once per nozzle.
+// Call after setting nozzle_diameter to more than one nozzle.
+void size_flush_to_nozzles(DynamicPrintConfig &config);
+
 // Apply `meshes` and config to `print`/`model`, each object with `instances` copies; optional per-object overrides,
 // auto-arranged unless `arrange` is false.
 void init_print(std::vector<TriangleMesh> &&meshes, Slic3r::Print &print, Slic3r::Model &model, const DynamicPrintConfig &config_in,
diff --git a/tests/fff_print/test_imex_mode_gcode.cpp b/tests/fff_print/test_imex_mode_gcode.cpp
index 04643864e7..d9772a1ea6 100644
--- a/tests/fff_print/test_imex_mode_gcode.cpp
+++ b/tests/fff_print/test_imex_mode_gcode.cpp
@@ -114,6 +114,7 @@ static void imex_7x4_printer(DynamicPrintConfig &config)
         // compares the two scripts and nothing else.
         { "gcode_flavor",              "klipper" },
     });
+    size_flush_to_nozzles(config);
 }
 
 // Set the mode scripts positionally, one per name in imex_mode_names. Assigning the vector
diff --git a/tests/fff_print/test_imex_slice_offset.cpp b/tests/fff_print/test_imex_slice_offset.cpp
index c12c0f20cb..03477dff7d 100644
--- a/tests/fff_print/test_imex_slice_offset.cpp
+++ b/tests/fff_print/test_imex_slice_offset.cpp
@@ -173,6 +173,7 @@ static void imex_printer(DynamicPrintConfig &config)
         { "initial_layer_print_height","0.2" },
         { "gcode_flavor",              "klipper" },
     });
+    size_flush_to_nozzles(config);
 }
 
 // Route every region to one filament. An unset *_filament_id is not "inherit":
diff --git a/tests/fff_print/test_multifilament.cpp b/tests/fff_print/test_multifilament.cpp
index 9f4f34dcc9..fc24268b0a 100644
--- a/tests/fff_print/test_multifilament.cpp
+++ b/tests/fff_print/test_multifilament.cpp
@@ -741,6 +741,7 @@ static void imex_7x4_printer(DynamicPrintConfig &config)
         // "G10 S<t> P<n>" from the same code, so the flavor is pinned rather than defaulted.
         { "gcode_flavor",              "klipper" },
     });
+    size_flush_to_nozzles(config);
 }
 
 // Route every region to one filament. An unset *_filament_id is not "inherit":