diff --git a/pcbnew/connectivity_algo.cpp b/pcbnew/connectivity_algo.cpp
index acac2d55e2..52384923b8 100644
--- a/pcbnew/connectivity_algo.cpp
+++ b/pcbnew/connectivity_algo.cpp
@@ -32,6 +32,10 @@
 #include <profile.h>
 #endif
 
+#ifdef USE_OPENMP
+#include <omp.h>
+#endif /* USE_OPENMP */
+
 using namespace std::placeholders;
 
 bool operator<( const CN_ANCHOR_PTR& a, const CN_ANCHOR_PTR& b )
@@ -521,7 +525,8 @@ void CN_CONNECTIVITY_ALGO::searchConnections( bool aIncludeZones )
         }
 
         #ifdef USE_OPENMP
-            #pragma omp parallel
+            // launch at least two threads, one to compute, second to update UI
+            #pragma omp parallel num_threads( std::max( omp_get_num_procs(), 2 ) )
         #endif
         {
             #ifdef USE_OPENMP
diff --git a/pcbnew/zone_filler.cpp b/pcbnew/zone_filler.cpp
index 327df69de6..7797e4a81d 100644
--- a/pcbnew/zone_filler.cpp
+++ b/pcbnew/zone_filler.cpp
@@ -116,7 +116,8 @@ void ZONE_FILLER::Fill( std::vector<ZONE_CONTAINER*> aZones )
 
 
     #ifdef USE_OPENMP
-        #pragma omp parallel
+        // launch at least two threads, one to compute, second to update UI
+        #pragma omp parallel num_threads( std::max( omp_get_num_procs(), 2 ) )
     #endif
     {
         #ifdef USE_OPENMP
@@ -177,7 +178,8 @@ void ZONE_FILLER::Fill( std::vector<ZONE_CONTAINER*> aZones )
         m_progressReporter->SetMaxProgress( toFill.size() );
     }
     #ifdef USE_OPENMP
-        #pragma omp parallel
+        // launch at least two threads, one to compute, second to update UI
+        #pragma omp parallel num_threads( std::max( omp_get_num_procs(), 2 ) )
     #endif
     {
         #ifdef USE_OPENMP