diff --git a/lib/nghttp2_hd.c b/lib/nghttp2_hd.c
index 054944d3..144b7db3 100644
--- a/lib/nghttp2_hd.c
+++ b/lib/nghttp2_hd.c
@@ -462,15 +462,13 @@ static int ensure_write_buffer(uint8_t **buf_ptr, size_t *buflen_ptr,
 
 static size_t count_encoded_length(size_t n, int prefix)
 {
+  size_t k = (1 << prefix) - 1;
   size_t len = 0;
-  if(prefix > 0) {
-    size_t k = (1 << prefix) - 1;
-    if(n >= k) {
-      n -= k;
-      ++len;
-    } else {
-      return 1;
-    }
+  if(n >= k) {
+    n -= k;
+    ++len;
+  } else {
+    return 1;
   }
   do {
     ++len;
@@ -485,17 +483,15 @@ static size_t count_encoded_length(size_t n, int prefix)
 
 static size_t encode_length(uint8_t *buf, size_t n, int prefix)
 {
+  size_t k = (1 << prefix) - 1;
   size_t len = 0;
-  if(prefix > 0) {
-    size_t k = (1 << prefix) - 1;
-    if(n >= k) {
-      *buf++ = k;
-      n -= k;
-      ++len;
-    } else {
-      *buf++ = n;
-      return 1;
-    }
+  if(n >= k) {
+    *buf++ = k;
+    n -= k;
+    ++len;
+  } else {
+    *buf++ = n;
+    return 1;
   }
   do {
     ++len;
@@ -528,17 +524,13 @@ static  uint8_t* decode_length(ssize_t *res, uint8_t *in, uint8_t *last,
     *res = -1;
     return in;
   }
-  if(prefix > 0) {
-    if((*in & k) == k) {
-      *res = k;
-    } else {
-      *res = (*in) & k;
-      return in + 1;
-    }
-    ++in;
+  if((*in & k) == k) {
+    *res = k;
   } else {
-    *res = 0;
+    *res = (*in) & k;
+    return in + 1;
   }
+  ++in;
   for(r = 0; in != last; ++in, r += 7) {
     *res += (*in & 0x7f) << r;
     if(*res >= (1 << 16)) {
@@ -549,7 +541,7 @@ static  uint8_t* decode_length(ssize_t *res, uint8_t *in, uint8_t *last,
       break;
     }
   }
-  if(*in & (1 << 7)) {
+  if(in == last || *in & (1 << 7)) {
     *res = -1;
     return NULL;
   } else {
@@ -584,14 +576,14 @@ static int emit_indname_block(uint8_t **buf_ptr, size_t *buflen_ptr,
   uint8_t *bufp;
   size_t encvallen = nghttp2_hd_huff_encode_count(value, valuelen, side);
   size_t blocklen = count_encoded_length(index + 1, 6) +
-    count_encoded_length(encvallen, 0) + encvallen;
+    count_encoded_length(encvallen, 8) + encvallen;
   rv = ensure_write_buffer(buf_ptr, buflen_ptr, *offset_ptr, blocklen);
   if(rv != 0) {
     return rv;
   }
   bufp = *buf_ptr + *offset_ptr;
   bufp += encode_length(bufp, index + 1, 6);
-  bufp += encode_length(bufp, encvallen, 0);
+  bufp += encode_length(bufp, encvallen, 8);
   nghttp2_hd_huff_encode(bufp, *buflen_ptr - (bufp - *buf_ptr),
                          value, valuelen, side);
   if(!inc_indexing) {
@@ -613,19 +605,19 @@ static int emit_newname_block(uint8_t **buf_ptr, size_t *buflen_ptr,
     nghttp2_hd_huff_encode_count(nv->name, nv->namelen, side);
   size_t encvallen =
     nghttp2_hd_huff_encode_count(nv->value, nv->valuelen, side);
-  size_t blocklen = 1 + count_encoded_length(encnamelen, 0) + encnamelen +
-    count_encoded_length(encvallen, 0) + encvallen;
+  size_t blocklen = 1 + count_encoded_length(encnamelen, 8) + encnamelen +
+    count_encoded_length(encvallen, 8) + encvallen;
   rv = ensure_write_buffer(buf_ptr, buflen_ptr, *offset_ptr, blocklen);
   if(rv != 0) {
     return rv;
   }
   bufp = *buf_ptr + *offset_ptr;
   *bufp++ = inc_indexing ? 0 : 0x40u;
-  bufp += encode_length(bufp, encnamelen, 0);
+  bufp += encode_length(bufp, encnamelen, 8);
   nghttp2_hd_huff_encode(bufp, *buflen_ptr - (bufp - *buf_ptr),
                          nv->name, nv->namelen, side);
   bufp += encnamelen;
-  bufp += encode_length(bufp, encvallen, 0);
+  bufp += encode_length(bufp, encvallen, 8);
   nghttp2_hd_huff_encode(bufp, *buflen_ptr - (bufp - *buf_ptr),
                          nv->value, nv->valuelen, side);
   *offset_ptr += blocklen;
@@ -988,7 +980,7 @@ ssize_t nghttp2_hd_inflate_hd(nghttp2_hd_context *inflater,
         rv = NGHTTP2_ERR_HEADER_COMP;
         goto fail;
       }
-      in = decode_length(&namelen, in, last, 0);
+      in = decode_length(&namelen, in, last, 8);
       if(namelen < 0 || in + namelen > last) {
         rv = NGHTTP2_ERR_HEADER_COMP;
         goto fail;
@@ -1006,7 +998,7 @@ ssize_t nghttp2_hd_inflate_hd(nghttp2_hd_context *inflater,
         goto fail;
       }
 
-      in = decode_length(&valuelen, in, last, 0);
+      in = decode_length(&valuelen, in, last, 8);
       if(valuelen < 0 || in + valuelen > last) {
         free(nv.name);
         rv =  NGHTTP2_ERR_HEADER_COMP;
@@ -1057,7 +1049,7 @@ ssize_t nghttp2_hd_inflate_hd(nghttp2_hd_context *inflater,
         goto fail;
       }
       ent = nghttp2_hd_table_get(inflater, index);
-      in = decode_length(&valuelen, in , last, 0);
+      in = decode_length(&valuelen, in , last, 8);
       if(valuelen < 0 || in + valuelen > last) {
         rv = NGHTTP2_ERR_HEADER_COMP;
         goto fail;
diff --git a/lib/nghttp2_session.c b/lib/nghttp2_session.c
index 7eb6b642..048b0a2a 100644
--- a/lib/nghttp2_session.c
+++ b/lib/nghttp2_session.c
@@ -1597,11 +1597,16 @@ int nghttp2_session_send(nghttp2_session *session)
         return NGHTTP2_ERR_CALLBACK_FAILURE;
       }
     } else {
-      session->aob.framebufoff += sentlen;
-      if(session->aob.item->frame_cat == NGHTTP2_CAT_DATA) {
+      if(session->aob.item->frame_cat == NGHTTP2_CAT_DATA &&
+         session->aob.framebufoff + sentlen > NGHTTP2_FRAME_HEAD_LENGTH) {
         nghttp2_data *frame;
         nghttp2_stream *stream;
-        uint16_t len = nghttp2_get_uint16(&session->aob.framebuf[0]);
+        uint16_t len;
+        if(session->aob.framebufoff < NGHTTP2_FRAME_HEAD_LENGTH) {
+          len = session->aob.framebufoff + sentlen - NGHTTP2_FRAME_HEAD_LENGTH;
+        } else {
+          len = sentlen;
+        }
         frame = nghttp2_outbound_item_get_data_frame(session->aob.item);
         stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
         if(stream && stream->remote_flow_control) {
@@ -1611,6 +1616,7 @@ int nghttp2_session_send(nghttp2_session *session)
           session->remote_window_size -= len;
         }
       }
+      session->aob.framebufoff += sentlen;
       if(session->aob.framebufoff == session->aob.framebuflen) {
         /* Frame has completely sent */
         r = nghttp2_session_after_frame_sent(session);
diff --git a/tests/nghttp2_session_test.c b/tests/nghttp2_session_test.c
index a96498fd..458e229d 100644
--- a/tests/nghttp2_session_test.c
+++ b/tests/nghttp2_session_test.c
@@ -68,6 +68,7 @@ typedef struct {
   int data_chunk_recv_cb_called;
   int data_recv_cb_called;
   const nghttp2_frame *frame;
+  size_t fixed_sendlen;
 } my_user_data;
 
 static void scripted_data_feed_init(scripted_data_feed *df,
@@ -94,6 +95,15 @@ static ssize_t fail_send_callback(nghttp2_session *session,
   return NGHTTP2_ERR_CALLBACK_FAILURE;
 }
 
+static ssize_t fixed_bytes_send_callback(nghttp2_session *session,
+                                         const uint8_t *data, size_t len,
+                                         int flags, void *user_data)
+{
+  size_t fixed_sendlen = ((my_user_data*)user_data)->fixed_sendlen;
+  return fixed_sendlen < len ? fixed_sendlen : len;
+}
+
+
 static ssize_t scripted_recv_callback(nghttp2_session *session,
                                       uint8_t* data, size_t len, int flags,
                                       void *user_data)
@@ -2979,12 +2989,15 @@ void test_nghttp2_session_flow_control(void)
   nghttp2_frame settings_frame;
 
   memset(&callbacks, 0, sizeof(nghttp2_session_callbacks));
-  callbacks.send_callback = null_send_callback;
+  callbacks.send_callback = fixed_bytes_send_callback;
   callbacks.on_frame_send_callback = on_frame_send_callback;
   data_prd.read_callback = fixed_length_data_source_read_callback;
 
   ud.frame_send_cb_called = 0;
   ud.data_source_length = 128*1024;
+  /* Use smaller emission count so that we can check outbound flow
+     control window calculation is correct. */
+  ud.fixed_sendlen = 2*1024;
 
   /* Initial window size to 64KiB - 1*/
   nghttp2_session_client_new(&session, &callbacks, &ud);