diff --git a/xs/src/libslic3r/PrintConfig.cpp b/xs/src/libslic3r/PrintConfig.cpp
index 6aace7732..6f3c459b2 100644
--- a/xs/src/libslic3r/PrintConfig.cpp
+++ b/xs/src/libslic3r/PrintConfig.cpp
@@ -1292,8 +1292,12 @@ PrintConfigDef::PrintConfigDef()
     def->readonly = true;
     def->min = 1;
     def->max = 16;
-    def->default_value = new ConfigOptionInt((boost::thread::hardware_concurrency() == 0) ? 2 : boost::thread::hardware_concurrency());
-
+    {
+        int threads = boost::thread::hardware_concurrency();
+        if (threads == 0) threads = 2;
+        def->default_value = new ConfigOptionInt(threads);
+    }
+    
     def = this->add("toolchange_gcode", coString);
     def->label = "Tool change G-code";
     def->tooltip = "This custom code is inserted right before every extruder change. Note that you can use placeholder variables for all Slic3r settings as well as [previous_extruder] and [next_extruder].";
diff --git a/xs/src/libslic3r/libslic3r.h b/xs/src/libslic3r/libslic3r.h
index 77d30489d..89db6d81e 100644
--- a/xs/src/libslic3r/libslic3r.h
+++ b/xs/src/libslic3r/libslic3r.h
@@ -4,6 +4,7 @@
 // this needs to be included early for MSVC (listing it in Build.PL is not enough)
 #include <ostream>
 #include <iostream>
+#include <math.h>
 #include <queue>
 #include <sstream>
 #include <cstdio>
@@ -119,9 +120,10 @@ template <class T> void
 parallelize(std::queue<T> queue, boost::function<void(T)> func,
     int threads_count = boost::thread::hardware_concurrency())
 {
+    if (threads_count == 0) threads_count = 2;
     boost::mutex queue_mutex;
     boost::thread_group workers;
-    for (int i = 0; i < threads_count; i++)
+    for (int i = 0; i < fminf(threads_count, queue.size()); i++)
         workers.add_thread(new boost::thread(&_parallelize_do<T>, &queue, &queue_mutex, func));
     workers.join_all();
 }