diff --git a/README.md b/README.md
index b63e901..fd1b9b2 100644
--- a/README.md
+++ b/README.md
@@ -13,7 +13,7 @@ which will place a binary at `build/nstrophy`.
 
 The syntax for the execution of Nstrophy is
 ```bash
-./build/nstrophy [-p parameters] [-s savefile] [-u u_outfile] <command>
+./build/nstrophy [-p parameters] [-s savefile] [-u u_outfile] [-t nthreads] <command>
 ```
 * `parameters` is a list of parameters for the computation, see
   [Parameters](#parameters)
@@ -26,6 +26,8 @@ The syntax for the execution of Nstrophy is
 * `u_outfile` is a file to which the final u is written in plain text format,
   which can be used as an initial condition for a future computation.
 
+* `nthreads` is the number of threads used to compute Fast Fourier Transforms.
+
 Nstrophy is written in C. The Makefile uses the GNU C Compiler.
 
 Nstrophy depends on `fftw`: [https://fftw.org]