diff --git a/test/twotonetest.c b/test/twotonetest.c
index bb44498..66a0b63 100644
--- a/test/twotonetest.c
+++ b/test/twotonetest.c
@@ -85,7 +85,13 @@ double two_tone_test( int nfft, int bin1,int bin2)
 int main(int argc,char ** argv)
 {
     int nfft = 4*2*2*3*5;
-    if (argc>1) nfft = atoi(argv[1]);
+    if (argc>1) {
+        nfft = atoi(argv[1]);
+        if (nfft <= 0) {
+            fprintf(stderr,"Error: nfft must be a positive integer\n");
+            return 1;
+        }
+    }
 
     int i,j;
     double minsnr = 500;