diff --git a/tests/nghttp2_frame_test.c b/tests/nghttp2_frame_test.c
index 3c620e37..7a712fc6 100644
--- a/tests/nghttp2_frame_test.c
+++ b/tests/nghttp2_frame_test.c
@@ -138,7 +138,7 @@ void test_nghttp2_frame_pack_headers_frame_too_large(void)
   ssize_t nvlen;
   size_t big_vallen = NGHTTP2_MAX_HD_VALUE_LENGTH;
   char *big_hds[17];
-  size_t big_hdslen = sizeof(big_hds)/sizeof(big_hds[0]);
+  size_t big_hdslen = sizeof(big_hds)/sizeof(big_hds[0]) - 1;
   size_t i;
 
   for(i = 0; i < big_hdslen; i += 2) {
@@ -147,7 +147,7 @@ void test_nghttp2_frame_pack_headers_frame_too_large(void)
     memset(big_hds[i+1], '0'+i, big_vallen);
     big_hds[i+1][big_vallen] = '\0';
   }
-  big_hds[big_hdslen - 1] = NULL;
+  big_hds[big_hdslen] = NULL;
 
   nvlen = nghttp2_nv_array_from_cstr(&nva, (const char**)big_hds);
   nghttp2_hd_deflate_init(&deflater, NGHTTP2_HD_SIDE_CLIENT);
diff --git a/tests/nghttp2_session_test.c b/tests/nghttp2_session_test.c
index 37b5be77..738fa0dd 100644
--- a/tests/nghttp2_session_test.c
+++ b/tests/nghttp2_session_test.c
@@ -1376,7 +1376,7 @@ void test_nghttp2_session_send_headers_header_comp_error(void)
   ssize_t nvlen;
   size_t vallen = NGHTTP2_MAX_HD_VALUE_LENGTH;
   char *nv[17];
-  size_t nnv = sizeof(nv)/sizeof(nv[0]);
+  size_t nnv = sizeof(nv)/sizeof(nv[0]) - 1;
   size_t i;
 
   for(i = 0; i < nnv; i += 2) {
@@ -1385,7 +1385,7 @@ void test_nghttp2_session_send_headers_header_comp_error(void)
     memset(nv[i+1], '0'+i, vallen);
     nv[i+1][vallen] = '\0';
   }
-  nv[nnv - 1] = NULL;
+  nv[nnv] = NULL;
 
   memset(&callbacks, 0, sizeof(nghttp2_session_callbacks));
   callbacks.send_callback = null_send_callback;