diff --git a/src/inspector_socket.cc b/src/inspector_socket.cc
index 52e53373c93adc..970df7cd8db871 100644
--- a/src/inspector_socket.cc
+++ b/src/inspector_socket.cc
@@ -360,7 +360,10 @@ static ws_decode_result decode_frame_hybi17(const std::vector<char>& buffer,
   }
   size_t payload_length = static_cast<size_t>(payload_length64);
 
-  if (buffer.size() - kMaskingKeyWidthInBytes < payload_length)
+  // The masking key and the payload follow the header `it` already walked
+  // past, so they have to fit in what is left rather than in the whole buffer.
+  size_t remaining = static_cast<size_t>(buffer.end() - it);
+  if (remaining < kMaskingKeyWidthInBytes + payload_length)
     return FRAME_INCOMPLETE;
 
   std::vector<char>::const_iterator masking_key = it;
diff --git a/test/cctest/test_inspector_socket.cc b/test/cctest/test_inspector_socket.cc
index 2efa0d55d748f1..9282eb4712ff32 100644
--- a/test/cctest/test_inspector_socket.cc
+++ b/test/cctest/test_inspector_socket.cc
@@ -409,6 +409,31 @@ TEST_F(InspectorSocketTest, ReadsAndWritesInspectorMessage) {
                          reinterpret_cast<uv_handle_t*>(&client_socket)));
 }
 
+TEST_F(InspectorSocketTest, WaitsForFrameBodyToArrive) {
+  do_write(const_cast<char*>(HANDSHAKE_REQ), sizeof(HANDSHAKE_REQ) - 1);
+  expect_handshake();
+
+  // A header announcing a masked five byte payload, with the masking key and
+  // the payload still on the wire. The frame has to be treated as incomplete
+  // until the remaining bytes show up.
+  const char FRAME_HEADER[] = {'\x81', '\x85'};
+  do_write(FRAME_HEADER, sizeof(FRAME_HEADER));
+
+  // Round trip through the server so the header is guaranteed to have been
+  // read on its own, instead of arriving together with the body below.
+  const char SERVER_MESSAGE[] = "ping";
+  const char SERVER_FRAME[] = {'\x81', '\x04', 'p', 'i', 'n', 'g'};
+  delegate->Write(SERVER_MESSAGE, sizeof(SERVER_MESSAGE) - 1);
+  expect_on_client(SERVER_FRAME, sizeof(SERVER_FRAME));
+
+  const char FRAME_BODY[] = {'\x01', '\x02', '\x03', '\x04',
+                             '\x69', '\x67', '\x6F', '\x68', '\x6E'};
+  do_write(FRAME_BODY, sizeof(FRAME_BODY));
+
+  const char CLIENT_MESSAGE[] = "hello";
+  delegate->ExpectData(CLIENT_MESSAGE, sizeof(CLIENT_MESSAGE) - 1);
+}
+
 TEST_F(InspectorSocketTest, BufferEdgeCases) {
   do_write(const_cast<char*>(HANDSHAKE_REQ), sizeof(HANDSHAKE_REQ) - 1);
   expect_handshake();