diff --git a/src/maths/fft/fftext.c b/src/maths/fft/fftext.c
index d8f1ba13f..2a9cb64a0 100644
--- a/src/maths/fft/fftext.c
+++ b/src/maths/fft/fftext.c
@@ -17,6 +17,10 @@
 #include "ngspice/fftext.h"
 #include "ngspice/memory.h"
 
+#ifndef M_PI
+#define M_PI		3.141592653589793238462643383279502884197	// pi
+#endif
+
 #define eq(a,b)  (!strcmp((a), (b)))
 
 // pointers to storage of Utbl's and  BRLow's