diff --git a/hadamard_decoder.hh b/hadamard_decoder.hh
index 45a2a30..3da8548 100644
--- a/hadamard_decoder.hh
+++ b/hadamard_decoder.hh
@@ -16,7 +16,7 @@ public:
 	int operator()(const int8_t *code)
 	{
 		int sum[N];
-		for (int i = 0; i < N; i += 2) {
+		for (int i = 0; i < N-1; i += 2) {
 			sum[i] = code[i] + code[i+1];
 			sum[i+1] = code[i] - code[i+1];
 		}
diff --git a/simplex_decoder.hh b/simplex_decoder.hh
index 1706465..72badeb 100644
--- a/simplex_decoder.hh
+++ b/simplex_decoder.hh
@@ -18,7 +18,7 @@ public:
 		int sum[W];
 		sum[0] = code[0];
 		sum[1] = -code[0];
-		for (int i = 1; i < W; i += 2) {
+		for (int i = 1; i < W-2; i += 2) {
 			sum[i+1] = code[i] + code[i+1];
 			sum[i+2] = code[i] - code[i+1];
 		}