diff --git a/src/libslic3r/GCode/GCodeProcessor.cpp b/src/libslic3r/GCode/GCodeProcessor.cpp
index 006595eb7..2b2c2cb51 100644
--- a/src/libslic3r/GCode/GCodeProcessor.cpp
+++ b/src/libslic3r/GCode/GCodeProcessor.cpp
@@ -1686,6 +1686,10 @@ bool GCodeProcessor::process_cura_tags(const std::string_view comment)
             BOOST_LOG_TRIVIAL(warning) << "GCodeProcessor found unknown extrusion role: " << type;
         }
 
+#if ENABLE_SEAMS_VISUALIZATION
+        if (m_extrusion_role == erExternalPerimeter)
+            m_seams_detector.activate(true);
+#endif // ENABLE_SEAMS_VISUALIZATION
         return true;
     }
 
@@ -1750,6 +1754,9 @@ bool GCodeProcessor::process_simplify3d_tags(const std::string_view comment)
     pos = cmt.find(" outer perimeter");
     if (pos == 0) {
         m_extrusion_role = erExternalPerimeter;
+#if ENABLE_SEAMS_VISUALIZATION
+        m_seams_detector.activate(true);
+#endif // ENABLE_SEAMS_VISUALIZATION
         return true;
     }
 
@@ -1904,6 +1911,11 @@ bool GCodeProcessor::process_craftware_tags(const std::string_view comment)
             BOOST_LOG_TRIVIAL(warning) << "GCodeProcessor found unknown extrusion role: " << type;
         }
 
+#if ENABLE_SEAMS_VISUALIZATION
+        if (m_extrusion_role == erExternalPerimeter)
+            m_seams_detector.activate(true);
+#endif // ENABLE_SEAMS_VISUALIZATION
+
         return true;
     }
 
@@ -1942,6 +1954,11 @@ bool GCodeProcessor::process_ideamaker_tags(const std::string_view comment)
             m_extrusion_role = erNone;
             BOOST_LOG_TRIVIAL(warning) << "GCodeProcessor found unknown extrusion role: " << type;
         }
+
+#if ENABLE_SEAMS_VISUALIZATION
+        if (m_extrusion_role == erExternalPerimeter)
+            m_seams_detector.activate(true);
+#endif // ENABLE_SEAMS_VISUALIZATION
         return true;
     }
 
@@ -2010,6 +2027,9 @@ bool GCodeProcessor::process_kissslicer_tags(const std::string_view comment)
     pos = comment.find(" 'Perimeter Path'");
     if (pos == 0) {
         m_extrusion_role = erExternalPerimeter;
+#if ENABLE_SEAMS_VISUALIZATION
+        m_seams_detector.activate(true);
+#endif // ENABLE_SEAMS_VISUALIZATION
         return true;
     }
 
@@ -2389,7 +2409,7 @@ void GCodeProcessor::process_G1(const GCodeReader::GCodeLine& line)
     if (type == EMoveType::Extrude && m_extrusion_role == erExternalPerimeter && m_seams_detector.is_active() && !m_seams_detector.has_first_vertex())
         m_seams_detector.set_first_vertex(m_result.moves.back().position - m_extruder_offsets[m_extruder_id]);
     // check for seam ending vertex and store the resulting move
-    else if ((type != EMoveType::Extrude || m_extrusion_role != erExternalPerimeter) && m_seams_detector.is_active()) {
+    else if ((type != EMoveType::Extrude || m_extrusion_role != erExternalPerimeter) && m_seams_detector.is_active() && m_seams_detector.has_first_vertex()) {
         auto set_end_position = [this](const Vec3f& pos) {
             m_end_position[X] = pos.x(); m_end_position[Y] = pos.y(); m_end_position[Z] = pos.z();
         };
@@ -2398,8 +2418,8 @@ void GCodeProcessor::process_G1(const GCodeReader::GCodeLine& line)
         const Vec3f curr_pos(m_end_position[X], m_end_position[Y], m_end_position[Z]);
         const Vec3f new_pos = m_result.moves.back().position - m_extruder_offsets[m_extruder_id];
         const std::optional<Vec3f> first_vertex = m_seams_detector.get_first_vertex();
-        // the threshold value = 0.25 is arbitrary, we may find some smarter condition later
-        if ((new_pos - *first_vertex).norm() < 0.25f) { 
+        // the threshold value = 0.0625f == 0.25 * 0.25 is arbitrary, we may find some smarter condition later
+        if ((new_pos - *first_vertex).squaredNorm() < 0.0625f) {
             set_end_position(0.5f * (new_pos + *first_vertex));
             store_move_vertex(EMoveType::Seam);
             set_end_position(curr_pos);