diff --git a/rtengine/FTblockDN.cc b/rtengine/FTblockDN.cc
index 50b178388..fadb74bac 100644
--- a/rtengine/FTblockDN.cc
+++ b/rtengine/FTblockDN.cc
@@ -71,6 +71,8 @@ namespace rtengine
 
 
 extern const Settings* settings;
+extern MyMutex *fftwMutex;
+
 
 void ImProcFunctions::Median_Denoise(float **src, float **dst, const int width, const int height, const Median medianType, const int iterations, const int numThreads, float **buffer)
 {
@@ -445,8 +447,7 @@ SSEFUNCTION void ImProcFunctions::RGB_denoise(int kall, Imagefloat * src, Imagef
         return;
     }
 
-    static MyMutex FftwMutex;
-    MyMutex::MyLock lock(FftwMutex);
+    MyMutex::MyLock lock(*fftwMutex);
 
     const nrquality nrQuality = (dnparams.smethod == "shal") ? QUALITY_STANDARD : QUALITY_HIGH;//shrink method
     const float qhighFactor = (nrQuality == QUALITY_HIGH) ? 1.f / static_cast<float>( settings->nrhigh) : 1.0f;
diff --git a/rtengine/init.cc b/rtengine/init.cc
index 6c1f4b98a..8d2cf9174 100644
--- a/rtengine/init.cc
+++ b/rtengine/init.cc
@@ -38,6 +38,7 @@ namespace rtengine
 const Settings* settings;
 
 MyMutex* lcmsMutex = nullptr;
+MyMutex *fftwMutex = nullptr;
 
 int init (const Settings* s, Glib::ustring baseDir, Glib::ustring userSettingsDir, bool loadAll)
 {
@@ -101,6 +102,7 @@ int init (const Settings* s, Glib::ustring baseDir, Glib::ustring userSettingsDi
     Color::init ();
     delete lcmsMutex;
     lcmsMutex = new MyMutex;
+    fftwMutex = new MyMutex;
     return 0;
 }
 
diff --git a/rtengine/tmo_fattal02.cc b/rtengine/tmo_fattal02.cc
index b44f1c1b6..0b9914e0f 100644
--- a/rtengine/tmo_fattal02.cc
+++ b/rtengine/tmo_fattal02.cc
@@ -74,6 +74,7 @@
 namespace rtengine {
 
 extern const Settings *settings;
+extern MyMutex *fftwMutex;
 
 using namespace std;
 
@@ -629,6 +630,7 @@ void tmo_fattal02(size_t width,
   Array2Df U(width, height);
   // if (fftsolver)
   {
+      MyMutex::MyLock lock(*fftwMutex);
       solve_pde_fft(&DivG, &U, multithread);//, ph);
   }
   // else