diff --git a/src/libslic3r/EdgeGrid.hpp b/src/libslic3r/EdgeGrid.hpp
index 780a1a06966..eccbb457758 100644
--- a/src/libslic3r/EdgeGrid.hpp
+++ b/src/libslic3r/EdgeGrid.hpp
@@ -209,7 +209,7 @@ class Grid
 		assert(ixb >= 0 && size_t(ixb) < m_cols);
 		assert(iyb >= 0 && size_t(iyb) < m_rows);
 		// Account for the end points.
-		if (! visitor(iy, ix) || (ix == ixb && iy == iyb))
+		if ((ix == ixb && iy == iyb) || ! visitor(iy, ix))
 			// Both ends fall into the same cell.
 			return;
 		// Raster the centeral part of the line.
diff --git a/src/libslic3r/GCode/CoolingBuffer.cpp b/src/libslic3r/GCode/CoolingBuffer.cpp
index 47022353f26..dd8020f9297 100644
--- a/src/libslic3r/GCode/CoolingBuffer.cpp
+++ b/src/libslic3r/GCode/CoolingBuffer.cpp
@@ -612,6 +612,8 @@ std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::
         if (*line_end == '\n')
             ++ line_end;
         CoolingLine line(0, line_start - gcode.c_str(), line_end - gcode.c_str());
+        if (line.length() == 0)
+            continue; // Empty line.
         if (boost::starts_with(sline, "G0 "))
             line.type = CoolingLine::TYPE_G0;
         else if (boost::starts_with(sline, "G1 "))
diff --git a/src/libslic3r/Polyline.cpp b/src/libslic3r/Polyline.cpp
index 6eccbc3800a..c6e534e7752 100644
--- a/src/libslic3r/Polyline.cpp
+++ b/src/libslic3r/Polyline.cpp
@@ -401,9 +401,18 @@ void ThickPolyline::clip_end(double distance)
 
 void ThickPolyline::start_at_index(int index)
 {
-    assert(index >= 0 && index < this->points.size());
-    assert(this->points.front() == this->points.back() && this->width.front() == this->width.back());
-    if (index != 0 && index + 1 != int(this->points.size()) && this->points.front() == this->points.back() && this->width.front() == this->width.back()) {
+    assert(index >= 0 && index < (int)this->points.size());
+
+    // Operate only on properly closed ThickPolylines
+    if (this->points.empty())
+        return;
+    if (!(this->points.front() == this->points.back() &&
+          !this->width.empty() && this->width.front() == this->width.back())) {
+        // Not a properly closed ThickPolyline — nothing to rotate.
+        return;
+    }
+
+    if (index != 0 && index + 1 != int(this->points.size())) {
         this->points.pop_back();
         assert(this->points.size() * 2 == this->width.size());
         std::rotate(this->points.begin(), this->points.begin() + index, this->points.end());
diff --git a/src/slic3r/GUI/DoubleSliderForLayers.cpp b/src/slic3r/GUI/DoubleSliderForLayers.cpp
index bead6e4a4ec..7caaffb337c 100644
--- a/src/slic3r/GUI/DoubleSliderForLayers.cpp
+++ b/src/slic3r/GUI/DoubleSliderForLayers.cpp
@@ -1045,10 +1045,14 @@ bool DSForLayers::is_wipe_tower_layer(int tick) const
         return false;
     if (tick == 0 || (tick == (int)m_values.size() - 1 && m_values[tick] > m_values[tick - 1]))
         return false;
-    if ((m_values[tick - 1] == m_values[tick + 1] && m_values[tick] < m_values[tick + 1]) ||
-        (tick > 0 && m_values[tick] < m_values[tick - 1]) ) // if there is just one wiping on the layer 
-        return true;
-
+    // Make sure we don't access past the end of m_values (tick+1 must be valid).
+    if (tick > 0) {
+        if (tick + 1 < (int)m_values.size() &&
+            m_values[tick - 1] == m_values[tick + 1] && m_values[tick] < m_values[tick + 1])
+            return true;
+        if (m_values[tick] < m_values[tick - 1]) // if there is just one wiping on the layer
+            return true;
+    }
     return false;
 }