diff --git a/CMakeLists.txt b/CMakeLists.txt
index e031694e..f52d6760 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -160,6 +160,8 @@ if(FFTW)
 		if(FFTW_THREADS)
 			add_definitions(-DPIP_FFTW_THREADSAFE)
 			list(APPEND LIBS fftw3_threads fftw3f_threads)
+		else()
+			message(WARNING "Building fftw3 without threadsafe")
 		endif()
 	endif()
 else()