diff --git a/src/h2load.cc b/src/h2load.cc
index fc183204..76e8649f 100644
--- a/src/h2load.cc
+++ b/src/h2load.cc
@@ -801,6 +801,7 @@ TimeStat<Duration> compute_time_stat(const std::vector<Duration> &samples) {
     a = na;
   }
 
+  assert(n > 0);
   res.mean = Duration(sum / n);
   res.sd = Duration(static_cast<typename Duration::rep>(sqrt(q / n)));
   res.within_sd = within_sd(samples, res.mean, res.sd);
diff --git a/src/http2.cc b/src/http2.cc
index b47787da..bba0464a 100644
--- a/src/http2.cc
+++ b/src/http2.cc
@@ -832,7 +832,7 @@ parse_next_link_header_once(const char *first, const char *last) {
     static constexpr size_t PLLEN = sizeof(PL) - 1;
     if (first + PLLEN == last) {
       if (std::equal(PL, PL + PLLEN, first, util::CaseCmp())) {
-        ok = true;
+        // ok = true;
         // this is the end of sequence
         return {{{url_first, url_last}}, last};
       }
@@ -842,7 +842,7 @@ parse_next_link_header_once(const char *first, const char *last) {
         if (!std::equal(PL, PL + PLLEN, first, util::CaseCmp())) {
           break;
         }
-        ok = true;
+        // ok = true;
         // skip including ','
         first += PLLEN + 1;
         return {{{url_first, url_last}}, first};
diff --git a/src/shrpx_spdy_upstream.cc b/src/shrpx_spdy_upstream.cc
index 57d8462b..c3431f87 100644
--- a/src/shrpx_spdy_upstream.cc
+++ b/src/shrpx_spdy_upstream.cc
@@ -167,6 +167,8 @@ void on_ctrl_recv_callback(spdylay_session *session, spdylay_frame_type type,
     size_t header_buffer = 0;
     for (size_t i = 0; nv[i]; i += 2) {
       ++num_headers;
+      // shut up scan-build
+      assert(nv[i + 1]);
       header_buffer += strlen(nv[i]) + strlen(nv[i + 1]);
     }