diff --git a/devtools/server/tests/unit/head_dbg.js b/devtools/server/tests/unit/head_dbg.js
index 70baa259198b..086f24cfaec7 100644
--- a/devtools/server/tests/unit/head_dbg.js
+++ b/devtools/server/tests/unit/head_dbg.js
@@ -802,9 +802,7 @@ function getSourceContent(sourceClient) {
  * @returns Promise<SourceClient>
  */
 async function getSource(threadClient, url) {
-  const {sources} = await threadClient.getSources();
-  const source = sources.find((s) => s.url === url);
-
+  const source = await getSourceForm(threadClient, url);
   if (source) {
     return threadClient.source(source);
   }
@@ -813,11 +811,15 @@ async function getSource(threadClient, url) {
 }
 
 async function getSourceById(threadClient, id) {
-  const { sources } = await threadClient.getSources();
-  const form = sources.find(source => source.actor == id);
+  const form = await getSourceFormById(threadClient, id);
   return threadClient.source(form);
 }
 
+async function getSourceForm(threadClient, url) {
+  const {sources} = await threadClient.getSources();
+  return sources.find((s) => s.url === url);
+}
+
 async function getSourceFormById(threadClient, id) {
   const { sources } = await threadClient.getSources();
   return sources.find(source => source.actor == id);
diff --git a/devtools/server/tests/unit/test_blackboxing-01.js b/devtools/server/tests/unit/test_blackboxing-01.js
index b93079a10c7a..01004fc0c489 100644
--- a/devtools/server/tests/unit/test_blackboxing-01.js
+++ b/devtools/server/tests/unit/test_blackboxing-01.js
@@ -30,6 +30,7 @@ const SOURCE_URL = "http://example.com/source.js";
 
 const testBlackBox = async function() {
   const packet = await executeOnNextTickAndWaitForPause(evalCode, gClient);
+
   const bpSource = await getSourceById(
     gThreadClient,
     packet.frame.where.actor
@@ -38,9 +39,9 @@ const testBlackBox = async function() {
   await setBreakpoint(bpSource, { line: 2 });
   await resume(gThreadClient);
 
-  const sourceClient = await getSource(gThreadClient, BLACK_BOXED_URL);
+  let sourceForm = await getSourceForm(gThreadClient, BLACK_BOXED_URL);
 
-  Assert.ok(!sourceClient.isBlackBoxed,
+  Assert.ok(!sourceForm.isBlackBoxed,
             "By default the source is not black boxed.");
 
   // Test that we can step into `doStuff` when we are not black boxed.
@@ -58,8 +59,10 @@ const testBlackBox = async function() {
     }
   );
 
-  await blackBox(sourceClient);
-  Assert.ok(sourceClient.isBlackBoxed);
+  const blackboxedSource = await getSource(gThreadClient, BLACK_BOXED_URL);
+  await blackBox(blackboxedSource);
+  sourceForm = await getSourceForm(gThreadClient, BLACK_BOXED_URL);
+  Assert.ok(sourceForm.isBlackBoxed);
 
   // Test that we step through `doStuff` when we are black boxed and its frame
   // doesn't show up.
@@ -81,8 +84,9 @@ const testBlackBox = async function() {
     }
   );
 
-  await unBlackBox(sourceClient);
-  Assert.ok(!sourceClient.isBlackBoxed);
+  await unBlackBox(blackboxedSource);
+  sourceForm = await getSourceForm(gThreadClient, BLACK_BOXED_URL);
+  Assert.ok(!sourceForm.isBlackBoxed);
 
   // Test that we can step into `doStuff` again.
   await runTest(
diff --git a/devtools/shared/client/source-client.js b/devtools/shared/client/source-client.js
index 89d84460b66e..d37b057d0c18 100644
--- a/devtools/shared/client/source-client.js
+++ b/devtools/shared/client/source-client.js
@@ -19,7 +19,6 @@ const noop = () => {};
  */
 function SourceClient(client, form) {
   this._form = form;
-  this._isBlackBoxed = form.isBlackBoxed;
   this._activeThread = client;
   this._client = client.client;
 }
@@ -28,9 +27,6 @@ SourceClient.prototype = {
   get _transport() {
     return this._client._transport;
   },
-  get isBlackBoxed() {
-    return this._isBlackBoxed;
-  },
   get actor() {
     return this._form.actor;
   },
@@ -51,15 +47,6 @@ SourceClient.prototype = {
     },
     {
       telemetry: "BLACKBOX",
-      after: function(response) {
-        if (!response.error) {
-          this._isBlackBoxed = true;
-          if (this._activeThread) {
-            this._activeThread.emit("blackboxchange", this);
-          }
-        }
-        return response;
-      },
     },
   ),
 
@@ -73,15 +60,6 @@ SourceClient.prototype = {
     },
     {
       telemetry: "UNBLACKBOX",
-      after: function(response) {
-        if (!response.error) {
-          this._isBlackBoxed = false;
-          if (this._activeThread) {
-            this._activeThread.emit("blackboxchange", this);
-          }
-        }
-        return response;
-      },
     },
   ),