diff --git a/xs/src/libslic3r/GCode/SpiralVase.cpp b/xs/src/libslic3r/GCode/SpiralVase.cpp
index 892d3b4ccd..8e8ae3075c 100644
--- a/xs/src/libslic3r/GCode/SpiralVase.cpp
+++ b/xs/src/libslic3r/GCode/SpiralVase.cpp
@@ -17,7 +17,7 @@ std::string SpiralVase::process_layer(const std::string &gcode)
     // If we're not going to modify G-code, just feed it to the reader
     // in order to update positions.
     if (!this->enable) {
-        this->_reader.parse(gcode, {});
+        this->_reader.parse_buffer(gcode);
         return gcode;
     }
     
@@ -30,7 +30,7 @@ std::string SpiralVase::process_layer(const std::string &gcode)
     {
         //FIXME Performance warning: This copies the GCodeConfig of the reader.
         GCodeReader r = this->_reader;  // clone
-        r.parse(gcode, [&total_layer_length, &layer_height, &z, &set_z]
+        r.parse_buffer(gcode, [&total_layer_length, &layer_height, &z, &set_z]
             (GCodeReader &reader, const GCodeReader::GCodeLine &line) {
             if (line.cmd_is("G1")) {
                 if (line.extruding(reader)) {
@@ -50,7 +50,7 @@ std::string SpiralVase::process_layer(const std::string &gcode)
     z -= layer_height;
     
     std::string new_gcode;
-    this->_reader.parse(gcode, [&new_gcode, &z, &layer_height, &total_layer_length]
+    this->_reader.parse_buffer(gcode, [&new_gcode, &z, &layer_height, &total_layer_length]
         (GCodeReader &reader, GCodeReader::GCodeLine line) {
         if (line.cmd_is("G1")) {
             if (line.has_z()) {
diff --git a/xs/src/libslic3r/GCodeReader.cpp b/xs/src/libslic3r/GCodeReader.cpp
index d1f56d9158..965b7ef8ec 100644
--- a/xs/src/libslic3r/GCodeReader.cpp
+++ b/xs/src/libslic3r/GCodeReader.cpp
@@ -20,14 +20,6 @@ void GCodeReader::apply_config(const DynamicPrintConfig &config)
     m_extrusion_axis = m_config.get_extrusion_axis()[0];
 }
 
-void GCodeReader::parse(const std::string &gcode, callback_t callback)
-{
-    std::istringstream ss(gcode);
-    std::string line;
-    while (std::getline(ss, line))
-        this->parse_line(line, callback);
-}
-
 const char* GCodeReader::parse_line_internal(const char *ptr, GCodeLine &gline, std::pair<const char*, const char*> &command)
 {
     PROFILE_FUNC();
diff --git a/xs/src/libslic3r/GCodeReader.hpp b/xs/src/libslic3r/GCodeReader.hpp
index e546abe0b7..102cbd27ad 100644
--- a/xs/src/libslic3r/GCodeReader.hpp
+++ b/xs/src/libslic3r/GCodeReader.hpp
@@ -73,7 +73,21 @@ public:
     GCodeReader() : m_verbose(false), m_extrusion_axis('E') { memset(m_position, 0, sizeof(m_position)); }
     void apply_config(const GCodeConfig &config);
     void apply_config(const DynamicPrintConfig &config);
-    void parse(const std::string &gcode, callback_t callback);
+
+    template<typename Callback>
+    void parse_buffer(const std::string &buffer, Callback callback)
+    {
+        const char *ptr = buffer.c_str();
+        GCodeLine gline;
+        while (*ptr != 0) {
+            gline.reset();
+            ptr = this->parse_line(ptr, gline, callback);
+        }
+    }
+
+    void parse_buffer(const std::string &buffer)
+        { this->parse_buffer(buffer, [](GCodeReader&, const GCodeReader::GCodeLine&){}); }
+
     template<typename Callback>
     const char* parse_line(const char *ptr, GCodeLine &gline, Callback &callback)
     {
@@ -83,9 +97,11 @@ public:
         update_coordinates(gline, cmd);
         return end;
     }
+
     template<typename Callback>
     void parse_line(const std::string &line, Callback callback)
         { GCodeLine gline; this->parse_line(line.c_str(), gline, callback); }
+
     void parse_file(const std::string &file, callback_t callback);
 
     float& x()       { return m_position[X]; }
diff --git a/xs/src/libslic3r/GCodeTimeEstimator.cpp b/xs/src/libslic3r/GCodeTimeEstimator.cpp
index 8478eb77de..ef0d65d7cf 100644
--- a/xs/src/libslic3r/GCodeTimeEstimator.cpp
+++ b/xs/src/libslic3r/GCodeTimeEstimator.cpp
@@ -142,7 +142,9 @@ namespace Slic3r {
 
   void GCodeTimeEstimator::calculate_time_from_text(const std::string& gcode)
   {
-    _parser.parse(gcode, boost::bind(&GCodeTimeEstimator::_process_gcode_line, this, _1, _2));
+    _parser.parse_buffer(gcode, 
+      [this](GCodeReader &reader, const GCodeReader::GCodeLine &line)
+        { this->_process_gcode_line(reader, line); });
     _calculate_time();
     reset();
   }
@@ -921,7 +923,9 @@ namespace Slic3r {
 
   void GCodeTimeEstimator::_planner_forward_pass_kernel(Block* prev, Block* curr)
   {
-    if (prev == nullptr)
+    if (prev == nullptr || curr == nullptr)
+//FIXME something is fishy here. Review and compare with the firmware.
+//    if (prev == nullptr)
       return;
 
     // If the previous block is an acceleration block, but it is not long enough to complete the