diff --git a/kiss_fft.h b/kiss_fft.h
index 3a89c9d..e799137 100644
--- a/kiss_fft.h
+++ b/kiss_fft.h
@@ -112,6 +112,10 @@ void kiss_fft_cleanup(void);
  */
 int kiss_fft_next_fast_size(int n);
 
+/* for real ffts, we need an even size */
+#define kiss_fftr_next_fast_size_real(n) \
+        (kiss_fft_next_fast_size( ((n)+1)>>1)<<1)
+
 #ifdef __cplusplus
 } 
 #endif