diff --git a/quic/core/http/http_decoder.cc b/quic/core/http/http_decoder.cc
index 1bcbfaa..ffd5c74 100644
--- a/quic/core/http/http_decoder.cc
+++ b/quic/core/http/http_decoder.cc
@@ -45,10 +45,17 @@
 HttpDecoder::~HttpDecoder() {}
 
 QuicByteCount HttpDecoder::ProcessInput(const char* data, QuicByteCount len) {
+  DCHECK_EQ(QUIC_NO_ERROR, error_);
+  DCHECK_NE(STATE_ERROR, state_);
+
   QuicDataReader reader(data, len);
   bool continue_processing = true;
-  while (continue_processing && error_ == QUIC_NO_ERROR &&
+  while (continue_processing &&
          (reader.BytesRemaining() != 0 || state_ == STATE_FINISH_PARSING)) {
+    // |continue_processing| must have been set to false upon error.
+    DCHECK_EQ(QUIC_NO_ERROR, error_);
+    DCHECK_NE(STATE_ERROR, state_);
+
     switch (state_) {
       case STATE_READING_FRAME_TYPE:
         ReadFrameType(&reader);
diff --git a/quic/core/http/http_decoder.h b/quic/core/http/http_decoder.h
index fa0a27b..515daae 100644
--- a/quic/core/http/http_decoder.h
+++ b/quic/core/http/http_decoder.h
@@ -124,10 +124,14 @@
   // visitor method returns false or an error occurs.  Returns the number of
   // bytes processed.  Does not process any input if called after an error.
   // Paused processing can be resumed by calling ProcessInput() again with the
-  // unprocessed portion of data.
+  // unprocessed portion of data.  Must not be called after an error has
+  // occurred.
   QuicByteCount ProcessInput(const char* data, QuicByteCount len);
 
+  // Returns an error code other than QUIC_NO_ERROR if and only if
+  // Visitor::OnError() has been called.
   QuicErrorCode error() const { return error_; }
+
   const std::string& error_detail() const { return error_detail_; }
 
  private:
diff --git a/quic/core/http/quic_receive_control_stream.cc b/quic/core/http/quic_receive_control_stream.cc
index e7efad1..9e166e0 100644
--- a/quic/core/http/quic_receive_control_stream.cc
+++ b/quic/core/http/quic_receive_control_stream.cc
@@ -141,7 +141,8 @@
 
 void QuicReceiveControlStream::OnDataAvailable() {
   iovec iov;
-  while (!reading_stopped() && sequencer()->PrefetchNextRegion(&iov)) {
+  while (!reading_stopped() && decoder_.error() == QUIC_NO_ERROR &&
+         sequencer()->PrefetchNextRegion(&iov)) {
     decoder_.ProcessInput(reinterpret_cast<const char*>(iov.iov_base),
                           iov.iov_len);
   }
diff --git a/quic/core/http/quic_spdy_stream.cc b/quic/core/http/quic_spdy_stream.cc
index 92138a4..b7522c0 100644
--- a/quic/core/http/quic_spdy_stream.cc
+++ b/quic/core/http/quic_spdy_stream.cc
@@ -623,7 +623,8 @@
   }
 
   iovec iov;
-  while (!reading_stopped() && sequencer()->PrefetchNextRegion(&iov)) {
+  while (!reading_stopped() && decoder_.error() == QUIC_NO_ERROR &&
+         sequencer()->PrefetchNextRegion(&iov)) {
     DCHECK(!sequencer()->IsClosed());
     decoder_.ProcessInput(reinterpret_cast<const char*>(iov.iov_base),
                           iov.iov_len);