diff --git a/src/include/ngspice/fftext.h b/src/include/ngspice/fftext.h
index 3266b4107..a7822077f 100644
--- a/src/include/ngspice/fftext.h
+++ b/src/include/ngspice/fftext.h
@@ -20,7 +20,7 @@ void fftFree(void);
 // release storage for all private cosine and bit reversed tables
 
 int
-fft_windows(char *window, double *win, double *time, double length, double maxt, double span, int order);
+fft_windows(char *window, double *win, double *time, int length, double maxt, double span, int order);
 // computes some popular window functions
 
 void ffts(double *data, int M, int Rows);
diff --git a/src/maths/fft/fftext.c b/src/maths/fft/fftext.c
index 2a9cb64a0..0486296a3 100644
--- a/src/maths/fft/fftext.c
+++ b/src/maths/fft/fftext.c
@@ -93,7 +93,7 @@ void fftFree(void)
 }
 
 int
-fft_windows(char *window, double *win, double *time, double length, double maxt, double span, int order)
+fft_windows(char *window, double *win, double *time, int length, double maxt, double span, int order)
 {
     int i;
     double sigma, scale;