diff --git a/lib/routes/api/speech-credentials.js b/lib/routes/api/speech-credentials.js
index 64cdbdd..50c64cb 100644
--- a/lib/routes/api/speech-credentials.js
+++ b/lib/routes/api/speech-credentials.js
@@ -924,15 +924,15 @@ router.get('/:sid/test', async(req, res) => {
         }
       }
     } else if (cred.vendor === 'speechmatics') {
-      const {api_key} = credential;
+      const {api_key, speechmatics_stt_uri} = credential;
       if (cred.use_for_stt) {
         try {
-          await testSpeechmaticsStt(logger, {api_key});
+          await testSpeechmaticsStt(logger, {api_key, speechmatics_stt_uri});
           results.stt.status = 'ok';
-          SpeechCredential.ttsTestResult(sid, true);
+          SpeechCredential.sttTestResult(sid, true);
         } catch (err) {
           results.stt = {status: 'fail', reason: err.message};
-          SpeechCredential.ttsTestResult(sid, false);
+          SpeechCredential.sttTestResult(sid, false);
         }
       }
     } else if (cred.vendor === 'playht') {
diff --git a/lib/utils/speech-utils.js b/lib/utils/speech-utils.js
index 4e0498b..523b132 100644
--- a/lib/utils/speech-utils.js
+++ b/lib/utils/speech-utils.js
@@ -83,11 +83,33 @@ const testSonioxStt = async(logger, credentials) => {
   });
 };
 
+/**
+ * speechmatics_stt_uri is stored as a bare hostname - eu2.rt.speechmatics.com and friends for
+ * the hosted service, or the hostname of an on-prem container - while the sdk wants a full url
+ * that it appends the language to. At call time the stored value is handed to
+ * mod_speechmatics_transcribe as SPEECHMATICS_HOST, which always dials wss on port 443 with a
+ * path of /v2, so test exactly that. Accepting a shape the runtime cannot dial (a full url, a
+ * port) would report a credential as good that then fails on every call, and quietly falling
+ * back to a default host would do the same for a credential that has lost the field - the
+ * feature server omits SPEECHMATICS_HOST entirely when it is unset, and the module then
+ * refuses to start the session.
+ */
+const speechmaticsRealtimeUrl = (speechmatics_stt_uri) => {
+  const host = (speechmatics_stt_uri || '').trim();
+  if (!host) throw new Error('speechmatics_stt_uri is not set on this speech credential');
+  if (!/^[a-z0-9.-]+$/i.test(host)) {
+    throw new Error(
+      `invalid speechmatics_stt_uri '${host}': expected a bare hostname, e.g. eu2.rt.speechmatics.com`);
+  }
+  return `wss://${host}/v2`;
+};
+
 const testSpeechmaticsStt = async(logger, credentials) => {
   const {api_key, speechmatics_stt_uri} = credentials;
+  const realtimeUrl = speechmaticsRealtimeUrl(speechmatics_stt_uri);
   return new Promise(async(resolve, reject) => {
     try {
-      const session = new RealtimeSession({ apiKey: api_key, realtimeUrl: speechmatics_stt_uri });
+      const session = new RealtimeSession({ apiKey: api_key, realtimeUrl });
       let transcription = '';
       session.addListener('Error', (error) => {
         reject(error);
@@ -1845,6 +1867,7 @@ module.exports = {
   testVerbioStt,
   getLanguagesAndVoicesForVendor,
   testSpeechmaticsStt,
+  speechmaticsRealtimeUrl,
   testCartesia,
   testVoxistStt,
   testOpenAiStt,
diff --git a/test/index.js b/test/index.js
index b9269d6..91bc003 100644
--- a/test/index.js
+++ b/test/index.js
@@ -10,6 +10,7 @@ require('./auth');
 require('./sbcs');
 require('./ms-teams');
 require('./speech-credentials');
+require('./speechmatics-url');
 require('./recent-calls');
 require('./users');
 require('./users-view-only');
diff --git a/test/speechmatics-url.js b/test/speechmatics-url.js
new file mode 100644
index 0000000..028ae8c
--- /dev/null
+++ b/test/speechmatics-url.js
@@ -0,0 +1,35 @@
+const test = require('tape');
+const {speechmaticsRealtimeUrl} = require('../lib/utils/speech-utils');
+
+/* the runtime hands speechmatics_stt_uri to mod_speechmatics_transcribe as a bare hostname and
+   always dials wss on 443 with a path of /v2, so anything else must fail the credential test
+   rather than pass against a url only the test can reach
+*/
+test('speechmatics-url', (t) => {
+  t.equal(speechmaticsRealtimeUrl('eu2.rt.speechmatics.com'),
+    'wss://eu2.rt.speechmatics.com/v2', 'builds the url the runtime dials');
+  t.equal(speechmaticsRealtimeUrl('wus.rt.speechmatics.com'),
+    'wss://wus.rt.speechmatics.com/v2', 'honors the configured region');
+  t.equal(speechmaticsRealtimeUrl('sm-container.internal'),
+    'wss://sm-container.internal/v2', 'accepts an on-prem hostname');
+  t.equal(speechmaticsRealtimeUrl('  neu.rt.speechmatics.com  '),
+    'wss://neu.rt.speechmatics.com/v2', 'trims surrounding whitespace');
+
+  for (const uri of [undefined, null, '', '   ']) {
+    t.throws(() => speechmaticsRealtimeUrl(uri), /is not set on this speech credential/,
+      `rejects a credential with no host: ${JSON.stringify(uri)}`);
+  }
+
+  for (const uri of [
+    'wss://eu2.rt.speechmatics.com/v2',
+    'https://eu2.rt.speechmatics.com',
+    'sm-container.internal:9000',
+    'eu2.rt.speechmatics.com/v2',
+    'my host'
+  ]) {
+    t.throws(() => speechmaticsRealtimeUrl(uri), /expected a bare hostname/,
+      `rejects a shape the runtime cannot dial: ${uri}`);
+  }
+
+  t.end();
+});