diff --git a/src/include/ngspice/fftext.h b/src/include/ngspice/fftext.h
index b45a6e845..2b2dacd49 100644
--- a/src/include/ngspice/fftext.h
+++ b/src/include/ngspice/fftext.h
@@ -110,6 +110,6 @@ void rspectprod(double *data1, double *data2, double *outdata, int N);
 //#define CACHEFILLMALLOC(n) malloc((n)+CACHELINEFILL)
 
 
-#ifndef GREEN
-static void fftext(double*, double*, long int, long int, int);
+#ifdef BOURKE
+static void fftext(double *x, double *y, long int n, long int nn, int dir);
 #endif
diff --git a/src/maths/fft/fftext.c b/src/maths/fft/fftext.c
index 19b15ae6a..d13c94247 100644
--- a/src/maths/fft/fftext.c
+++ b/src/maths/fft/fftext.c
@@ -250,7 +250,7 @@ void rspectprod(double *data1, double *data2, double *outdata, int N)
 }
 
 
-#ifndef GREEN
+#ifdef BOURKE
 
 static void
 fftext(double *x, double *y, long int n, long int nn, int dir)
@@ -339,4 +339,4 @@ fftext(double *x, double *y, long int n, long int nn, int dir)
     }
 }
 
-#endif /* GREEN */
+#endif /* BOURKE */