diff --git a/mpn/generic/mulmod_2expp1.c b/mpn/generic/mulmod_2expp1.c
index 11be795e..26307e1c 100644
--- a/mpn/generic/mulmod_2expp1.c
+++ b/mpn/generic/mulmod_2expp1.c
@@ -31,7 +31,7 @@ or implied, of William Hart.
 #include "mpir.h"
 #include "gmp-impl.h"
 #include "longlong.h"
-#include "fft\fft_tuning.h"
+#include "fft/fft_tuning.h"
 
 static mp_size_t mulmod_2expp1_table_n[FFT_N_NUM] = MULMOD_TAB;