diff --git a/README.md b/README.md
index eea7b38..3fe9235 100644
--- a/README.md
+++ b/README.md
@@ -186,6 +186,10 @@ Options:
 - `--branch=master`: Branch of OpenModelica
 - `--fmi=False`: Test FMI
 - `--output=''`: Result location
+- `--omplot=URL`: OMPlot page a failed verification links to, by default the
+  one on the playground. That page must be able to fetch the report's files, so
+  a report behind a login or on a private network needs its own copy
+  (see [below](#plotting-failed-verifications-in-a-private-report)).
 - `--libraries=~/.openmodelica/libraries/`: Location of Modelica libraries
 - `--extraflags=''`: Extra compiler flags.
 - `--extrasimflags=''`: Extra simulation flags.
@@ -211,6 +215,28 @@ Options:
                  `procCCompile` above for more insight into individual test
                  parallelization.
 
+### Plotting failed verifications in a private report
+
+The OMPlot page is static files and reads the result files in the browser, so
+it can be hosted with the report. Build it from
+[OpenModelica](https://github.com/OpenModelica/OpenModelica) (needs
+`rustup target add wasm32-unknown-unknown`):
+
+```sh
+R=OMCompiler/SimulationRuntime/rust
+W=OMCompiler/Compiler/OpenModelica.rs/wasm
+cargo run --release --manifest-path $R/openmodelica_result_web_embed/Cargo.toml \
+  --bin install-result-web -- $OUTPUT/../omplot-web/omplot
+cp $W/omplot/index.html $OUTPUT/../omplot-web/omplot/
+cp $W/plot.js $W/units.js $W/ui.js $W/theme.css $OUTPUT/../omplot-web/
+```
+
+`$OUTPUT` is the `--output` directory. Then run `test.py` with
+`--omplot=../../omplot-web/omplot/index.html`, relative to
+`$OUTPUT/<library>/<library>.html`, and serve the results over HTTP, e.g.
+`python3 -m http.server -d $OUTPUT/..`. A page opened from `file://` cannot fetch
+files, so there the link downloads the `.mat` file instead.
+
 ### Simulation timeouts
 
 A simulation is killed after `ulimitExe` seconds, 240 by default - 99.5% of the
diff --git a/library.html.tpl b/library.html.tpl
index 76b9ef2..da90853 100644
--- a/library.html.tpl
+++ b/library.html.tpl
@@ -58,11 +58,14 @@ Config: <pre>#config#</pre>
 <script>
 // A failed verification links its two .mat files (the differing variables of
 // the result and of the reference) to the OMPlot page, which plots the tube
-// comparison of each variable. The page needs absolute URLs.
-const omplot = 'https://playground.openmodelica.org/latest/omplot/';
-for (const a of document.querySelectorAll('a[data-omplot]')) {
-  const abs = (f) => encodeURIComponent(new URL(f, location.href).href);
-  a.href = omplot + '?result=' + abs(a.dataset.omplot + '.mat') + '&reference=' + abs(a.dataset.omplot + '.ref.mat');
+// comparison of each variable. The page needs absolute URLs. It cannot fetch
+// files from file://, so there the link stays a download of the .mat file.
+if (location.protocol !== 'file:') {
+  const omplot = new URL(#omplot#, location.href).href;
+  for (const a of document.querySelectorAll('a[data-omplot]')) {
+    const abs = (f) => encodeURIComponent(new URL(f, location.href).href);
+    a.href = omplot + '?result=' + abs(a.dataset.omplot + '.mat') + '&reference=' + abs(a.dataset.omplot + '.ref.mat');
+  }
 }
 </script>
 </body>
diff --git a/test.py b/test.py
index 18694fe..b17befb 100755
--- a/test.py
+++ b/test.py
@@ -49,6 +49,7 @@
 parser.add_argument('-v', '--verbose', action="store_true", help="Verbose mode.", default=False)
 parser.add_argument('--execAllTests', action="store_true", help="Force all tests to be executed", default=False)
 parser.add_argument('--noSync', action="store_true", help="Move files using python instead of rsync", default=False)
+parser.add_argument('--omplot', default='https://playground.openmodelica.org/latest/omplot/', help="OMPlot page a failed verification links to. A relative URL is resolved against the library's report page. The page must be able to fetch the report's files, so use a copy hosted with the report if that is private.")
 parser.add_argument('--timeout', default=0, help="=[value] timeout in seconds for each test, it overrides the timeout calculated by the script")
 parser.add_argument('--msysEnvironment', help = 'MSYS2 environment used by OpenModelica on Windows.',  default = 'ucrt64')
 parser.add_argument('--debug', action="store_true", help="turn on the DEBUG mode", default=False)
@@ -1643,7 +1644,8 @@ def publishLibrary(libname):
       (u"#Verification#", html.escape(str(numSucceeded[7]))),
       (u"#totalTime#", html.escape(str(datetime.timedelta(seconds=int(sum(s[3].get("exectime") or 0.0 for s in stats)))))),
       (u"#config#", html.escape(json.dumps(conf["configFromFile"], indent=1, sort_keys=True))),
-      (u"#testsHTML#", testsHTML)
+      (u"#testsHTML#", testsHTML),
+      (u"#omplot#", json.dumps(args.omplot))
     )
     open(os.path.join(stageRoot, "%s.html" % libname), "w").write(multiple_replace(htmltpl, *replacements))