diff --git a/src/util.cc b/src/util.cc
index 1ef77bf0..a5865606 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -1158,7 +1158,7 @@ uint64_t get_uint64(const uint8_t *data) {
   n += static_cast<uint64_t>(data[1]) << 48;
   n += static_cast<uint64_t>(data[2]) << 40;
   n += static_cast<uint64_t>(data[3]) << 32;
-  n += data[4] << 24;
+  n += static_cast<uint64_t>(data[4]) << 24;
   n += data[5] << 16;
   n += data[6] << 8;
   n += data[7];
diff --git a/src/util_test.cc b/src/util_test.cc
index 85c791f6..f424a0f6 100644
--- a/src/util_test.cc
+++ b/src/util_test.cc
@@ -394,12 +394,22 @@ void test_util_localtime_date(void) {
 }
 
 void test_util_get_uint64(void) {
-  auto v = std::array<unsigned char, 8>{
-      {0x01, 0x12, 0x34, 0x56, 0x78, 0x9a, 0xab, 0xbc}};
+  {
+    auto v = std::array<unsigned char, 8>{
+        {0x01, 0x12, 0x34, 0x56, 0xff, 0x9a, 0xab, 0xbc}};
 
-  auto n = util::get_uint64(v.data());
+    auto n = util::get_uint64(v.data());
 
-  CU_ASSERT(0x01123456789aabbcULL == n);
+    CU_ASSERT(0x01123456ff9aabbcULL == n);
+  }
+  {
+    auto v = std::array<unsigned char, 8>{
+        {0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}};
+
+    auto n = util::get_uint64(v.data());
+
+    CU_ASSERT(0xffffffffffffffffULL == n);
+  }
 }
 
 } // namespace shrpx