diff --git a/libavcodec/flacenc.c b/libavcodec/flacenc.c
index 3b01a3ba1a..f96bc29c72 100644
--- a/libavcodec/flacenc.c
+++ b/libavcodec/flacenc.c
@@ -608,13 +608,14 @@ static void compute_autocorr(const int32_t *data, int len, int lag,
                              double *autoc)
 {
     int i, j;
-    double tmp[len + lag];
+    double tmp[len + lag + 1];
     double *data1= tmp + lag;
 
     apply_welch_window(data, len, data1);
 
     for(j=0; j<lag; j++)
         data1[j-lag]= 0.0;
+    data1[len] = 0.0;
 
     for(j=0; j<lag; j+=2){
         double sum0 = 1.0, sum1 = 1.0;
@@ -628,8 +629,10 @@ static void compute_autocorr(const int32_t *data, int len, int lag,
 
     if(j==lag){
         double sum = 1.0;
-        for(i=0; i<len; i++)
-            sum += data1[i] * data1[i-j];
+        for(i=0; i<len; i+=2){
+            sum += data1[i  ] * data1[i-j  ]
+                 + data1[i+1] * data1[i-j+1];
+        }
         autoc[j] = sum;
     }
 }
@@ -757,7 +760,7 @@ static int lpc_calc_coefs(const int32_t *samples, int blocksize, int max_order,
     assert(max_order >= MIN_LPC_ORDER && max_order <= MAX_LPC_ORDER);
 
     if(use_lpc == 1){
-        compute_autocorr(samples, blocksize, max_order+1, autoc);
+        compute_autocorr(samples, blocksize, max_order, autoc);
 
         compute_lpc_coefs(autoc, max_order, lpc, ref);
     }else{