diff --git a/rtengine/FTblockDN.cc b/rtengine/FTblockDN.cc
index 565004e1d..c600b6d0c 100644
--- a/rtengine/FTblockDN.cc
+++ b/rtengine/FTblockDN.cc
@@ -85,7 +85,8 @@ namespace rtengine {
 
 	void ImProcFunctions::RGB_denoise(Imagefloat * src, Imagefloat * dst, bool isRAW, const procparams::DirPyrDenoiseParams & dnparams, const procparams::DefringeParams & defringe, const double expcomp)
 	{
-
+		static Glib::Mutex      FftwMutex;
+		FftwMutex.lock();
 		//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
 		/*if (plistener) {
@@ -736,6 +737,7 @@ namespace rtengine {
 	fftwf_destroy_plan( plan_forward_blox[1] );
 	fftwf_destroy_plan( plan_backward_blox[1] );
 	fftwf_cleanup();
+	FftwMutex.unlock();
 
 	}//end of main RGB_denoise