diff --git a/kiss_fft.c b/kiss_fft.c
index b0e47b2..79c9392 100644
--- a/kiss_fft.c
+++ b/kiss_fft.c
@@ -383,3 +383,17 @@ void kiss_fft_cleanup(void)
     tmpbuf=NULL;
     ntmpbuf=0;
 }
+
+int kiss_fft_next_fast_size(int n)
+{
+    while(1) {
+        int m=n;
+        while ( (m%2) == 0 ) m/=2;
+        while ( (m%3) == 0 ) m/=3;
+        while ( (m%5) == 0 ) m/=5;
+        if (m<=1)
+            break; /* n is completely factorable by twos, threes, and fives */
+        n++;
+    }
+    return n;
+}
diff --git a/kiss_fft.h b/kiss_fft.h
index f67963f..9e679ff 100644
--- a/kiss_fft.h
+++ b/kiss_fft.h
@@ -107,6 +107,11 @@ void kiss_fft_stride(kiss_fft_cfg cfg,const kiss_fft_cpx *fin,kiss_fft_cpx *fout
 void kiss_fft_cleanup(void);
 	
 
+/*
+ * Returns the smallest integer k, such that k>=n and k has only "fast" factors (2,3,5)
+ */
+int kiss_fft_next_fast_size(int n);
+
 #ifdef __cplusplus
 } 
 #endif
diff --git a/test/benchkiss.c b/test/benchkiss.c
index d379480..378eef5 100644
--- a/test/benchkiss.c
+++ b/test/benchkiss.c
@@ -23,6 +23,10 @@ int main(int argc,char ** argv)
       switch (c) {
       case 'n':
         nfft = atoi (optarg);
+        if (nfft != kiss_fft_next_fast_size(nfft) ) {
+            int ng = kiss_fft_next_fast_size(nfft);
+            fprintf(stderr,"warning: %d might be a better choice for speed than %d\n",ng,nfft);
+        }
         break;
       case 'x':
         numffts = atoi (optarg);
diff --git a/tools/kiss_fftnd.c b/tools/kiss_fftnd.c
index 8a5a93d..9cdf6af 100644
--- a/tools/kiss_fftnd.c
+++ b/tools/kiss_fftnd.c
@@ -73,7 +73,7 @@ kiss_fftnd_cfg kiss_fftnd_alloc(const int *dims,int ndims,int inverse_fft,void*m
         st->states[i] = kiss_fft_alloc (st->dims[i], inverse_fft, ptr,&len);
         ptr += len;
     }
-    if ( ptr - (char*)st != memneeded ) {
+    if ( ptr - (char*)st != (int)memneeded ) {
         fprintf(stderr,
                 "################################################################################\n"
                 "Internal error! Memory allocation miscalculation\n"