diff --git a/src/libslic3r/GCode/GCodeProcessor.cpp b/src/libslic3r/GCode/GCodeProcessor.cpp
index dc12925ab1..791efaf835 100644
--- a/src/libslic3r/GCode/GCodeProcessor.cpp
+++ b/src/libslic3r/GCode/GCodeProcessor.cpp
@@ -2624,7 +2624,7 @@ void GCodeProcessor::process_G1(const std::array<std::optional<double>, 4>& axes
 
     if (volume_extruded_filament != 0.)
         m_used_filaments.increase_caches(volume_extruded_filament, m_extruder_id, area_filament_cross_section * m_parking_position,
-                                        area_filament_cross_section * m_extra_loading_move);
+                                         area_filament_cross_section * m_extra_loading_move);
 
     const EMoveType type = move_type(delta_pos);
     if (type == EMoveType::Extrude) {
@@ -2638,9 +2638,16 @@ void GCodeProcessor::process_G1(const std::array<std::optional<double>, 4>& axes
 #endif // ENABLE_GCODE_VIEWER_DATA_CHECKING
 
         if (m_forced_height > 0.0f)
+            // use height coming from the gcode tags
             m_height = m_forced_height;
-        else if (m_layer_id == 0)
-            m_height = m_first_layer_height + m_z_offset;
+        else if (m_layer_id == 0) { // first layer
+            if (m_end_position[Z] > 0.0f)
+                // use the current (clamped) z, if greater than zero  
+                m_height = std::min<float>(m_end_position[Z], 2.0f);
+            else
+                // use the first layer height  
+                m_height = m_first_layer_height + m_z_offset;
+        }
         else if (origin == G1DiscretizationOrigin::G1) {
             if (m_end_position[Z] > m_extruded_last_z + EPSILON && delta_pos[Z] == 0.0)
                 m_height = m_end_position[Z] - m_extruded_last_z;
@@ -2649,9 +2656,6 @@ void GCodeProcessor::process_G1(const std::array<std::optional<double>, 4>& axes
         if (m_height == 0.0f)
             m_height = DEFAULT_TOOLPATH_HEIGHT;
 
-        if (m_end_position[Z] == 0.0f || (m_extrusion_role == GCodeExtrusionRole::Custom && m_layer_id == 0))
-            m_end_position[Z] = m_height;
-
         if (origin == G1DiscretizationOrigin::G1)
             m_extruded_last_z = m_end_position[Z];
         m_options_z_corrector.update(m_height);
@@ -2661,6 +2665,7 @@ void GCodeProcessor::process_G1(const std::array<std::optional<double>, 4>& axes
 #endif // ENABLE_GCODE_VIEWER_DATA_CHECKING
 
         if (m_forced_width > 0.0f)
+            // use width coming from the gcode tags
             m_width = m_forced_width;
         else if (m_extrusion_role == GCodeExtrusionRole::ExternalPerimeter)
             // cross section: rectangle
diff --git a/src/slic3r/GUI/GCodeViewer.cpp b/src/slic3r/GUI/GCodeViewer.cpp
index 14e73e0484..5cc55be5ff 100644
--- a/src/slic3r/GUI/GCodeViewer.cpp
+++ b/src/slic3r/GUI/GCodeViewer.cpp
@@ -2264,16 +2264,16 @@ void GCodeViewer::load_toolpaths(const GCodeProcessorResult& gcode_result)
             // layers zs/ranges
             const double* const last_z = m_layers.empty() ? nullptr : &m_layers.get_zs().back();
             const double z = static_cast<double>(move.position.z());
-            if (last_z == nullptr || z < *last_z - EPSILON || *last_z + EPSILON < z) {
+            if (move.extrusion_role != GCodeExtrusionRole::Custom &&
+                (last_z == nullptr || z < *last_z - EPSILON || *last_z + EPSILON < z)) {
                 // start a new layer
                 const size_t start_it = (m_layers.empty() && first_travel_s_id != 0) ? first_travel_s_id : last_travel_s_id;
                 m_layers.append(z, { start_it, move_id });
             }
-            else if (!move.internal_only) {
+            else if (!m_layers.empty() && !move.internal_only)
                 // update last layer
                 m_layers.get_ranges().back().last = move_id;
-            }
-            
+
             // extruder ids
             m_extruder_ids.emplace_back(move.extruder_id);
             // roles