diff --git a/docs/cmdline-opts/write-out.md b/docs/cmdline-opts/write-out.md
index df0d3d5c84..5cf9d91f87 100644
--- a/docs/cmdline-opts/write-out.md
+++ b/docs/cmdline-opts/write-out.md
@@ -202,7 +202,8 @@ The total amount of bytes that were downloaded. This is the size of the
 body/data that was transferred, excluding headers.
 
 ## `size_header`
-The total amount of bytes of the downloaded headers.
+The total amount of bytes of the downloaded headers, as represented in
+HTTP/1-style header format.
 
 ## `size_request`
 The total amount of bytes that were sent in the HTTP request.
diff --git a/docs/libcurl/opts/CURLINFO_HEADER_SIZE.md b/docs/libcurl/opts/CURLINFO_HEADER_SIZE.md
index c27856809e..f0ce241e3f 100644
--- a/docs/libcurl/opts/CURLINFO_HEADER_SIZE.md
+++ b/docs/libcurl/opts/CURLINFO_HEADER_SIZE.md
@@ -29,11 +29,15 @@ CURLcode curl_easy_getinfo(CURL *handle, CURLINFO_HEADER_SIZE, long *sizep);
 # DESCRIPTION
 
 Pass a pointer to a long to receive the total size of all the headers
-received. Measured in number of bytes.
+received, represented in HTTP/1-style header format. Measured in number of
+bytes.
 
 The total includes the size of any received headers suppressed by
 CURLOPT_SUPPRESS_CONNECT_HEADERS(3).
 
+The number of bytes transferred over the wire (or to the TLS backend) is
+different when using HTTP/2 or greater.
+
 # %PROTOCOLS%
 
 # EXAMPLE