diff --git a/changelog.md b/changelog.md
index ea22028397..d70a4367d8 100644
--- a/changelog.md
+++ b/changelog.md
@@ -2,6 +2,7 @@
 
 
 ## Changes affecting backward compatibility
+- `httpclient.contentLength` default to `-1` if the Content-Length header is not set in the response, it followed Apache HttpClient(Java), http(go) and .Net HttpWebResponse(C#) behavior. Previously raise `ValueError`.  
 
 - `addr` is now available for all addressable locations,
   `unsafeAddr` is now deprecated and an alias for `addr`.
diff --git a/lib/pure/httpclient.nim b/lib/pure/httpclient.nim
index dcd1f87d6c..405fadc2f9 100644
--- a/lib/pure/httpclient.nim
+++ b/lib/pure/httpclient.nim
@@ -274,9 +274,9 @@ proc contentLength*(response: Response | AsyncResponse): int =
   ## This is effectively the value of the "Content-Length" header.
   ##
   ## A `ValueError` exception will be raised if the value is not an integer.
-  var contentLengthHeader = response.headers.getOrDefault("Content-Length")
+  ## If the Content-Length header is not set in the response, ContentLength is set to the value -1.
+  var contentLengthHeader = response.headers.getOrDefault("Content-Length", @["-1"])
   result = contentLengthHeader.parseInt()
-  doAssert(result >= 0 and result <= high(int32))
 
 proc lastModified*(response: Response | AsyncResponse): DateTime =
   ## Retrieves the specified response's last modified time.