diff --git a/docs/tests/FILEFORMAT.md b/docs/tests/FILEFORMAT.md
index 26dae3e23f..5fe09aa3db 100644
--- a/docs/tests/FILEFORMAT.md
+++ b/docs/tests/FILEFORMAT.md
@@ -712,12 +712,17 @@ server is used), if `nonewline` is set, we cut off the trailing newline of
 this given data before comparing with the one actually sent by the client The
 `<strip>` and `<strippart>` rules are applied before comparisons are made.
 
-### `<stderr [mode="text"] [nonewline="yes"] [crlf="yes|headers"]>`
+### `<stderr [mode="text/warn"] [nonewline="yes"] [crlf="yes|headers"]>`
 This verifies that this data was passed to stderr.
 
 Use the mode="text" attribute if the output is in text mode on platforms that
 have a text/binary difference.
 
+Use the mode="warn" attribute if the output curl warning output, as it then
+makes the check without newlines and the prefix to better handle that the
+lines may wrap at different points depending on the lengths of the lines and
+terminal width.
+
 `crlf=yes` forces the newlines to become CRLF even if not written so in the
 test.
 
diff --git a/tests/data/test1712 b/tests/data/test1712
index 2466939ff2..198b5e17ad 100644
--- a/tests/data/test1712
+++ b/tests/data/test1712
@@ -53,7 +53,7 @@ Content-Type: application/x-www-form-urlencoded
 
 'arg-with-quote'
 </protocol>
-<stderr mode="text">
+<stderr mode="warn">
 Warning: %LOGDIR/config:1 Option 'data' uses argument with leading single quote.%SP
 Warning: It is probably a mistake. Consider double quotes.
 </stderr>
diff --git a/tests/runtests.pl b/tests/runtests.pl
index e0bc468f10..d8ac67a670 100755
--- a/tests/runtests.pl
+++ b/tests/runtests.pl
@@ -1346,6 +1346,14 @@ sub singletest_check {
             normalize_text(\@validstderr);
             normalize_text(\@actual);
         }
+        if($filemode && ($filemode eq "warn")) {
+            map { 's/Warning: //' } (@validstderr);
+            map { 's/\r//' } (@validstderr);
+            map { 's/\n/ /' } (@validstderr);
+            map { 's/Warning: //' } (@actual);
+            map { 's/\r//' } (@actual);
+            map { 's/\n/ /' } (@actual);
+        }
 
         if($hash{'nonewline'}) {
             # Yes, we must cut off the final newline from the final line