diff --git a/Makefile b/Makefile
index c24a72f0da948d7306ffdfd98a1d2e6896963478..1be9de63bac888db923ab4cb458a543e2d035cb3 100644
--- a/Makefile
+++ b/Makefile
@@ -38,7 +38,7 @@ OPT += -DUSE_FFTW
 OPT += -DHYBRID_FFTW
 
 # switch on the OpenMP parallelization
-OPT += USE_OMP
+OPT += -DUSE_OMP
 
 # write the full 3D cube of gridded visibilities and its FFT transform
 #OPT += -DWRITE_DATA