diff --git a/jobserver/forms.py b/jobserver/forms.py
index 63eae233e..0be1fc2e4 100644
--- a/jobserver/forms.py
+++ b/jobserver/forms.py
@@ -175,11 +175,6 @@ def clean(self):
             msg = "Unknown repo, please reload the page and try again"
             raise forms.ValidationError(msg)
 
-        # normalise branch names so we can do a case insensitive match
-        branches = [b.lower() for b in repo["branches"]]
-        if branch.lower() not in branches:
-            raise forms.ValidationError(f'Unknown branch "{branch}"')
-
     def clean_name(self):
         name = self.cleaned_data["name"].lower()
 
diff --git a/tests/unit/jobserver/test_forms.py b/tests/unit/jobserver/test_forms.py
index e08d308cb..ed683e39a 100644
--- a/tests/unit/jobserver/test_forms.py
+++ b/tests/unit/jobserver/test_forms.py
@@ -213,17 +213,16 @@ def test_workspacecreateform_unknown_branch_validation_fails():
             "branches": ["test-branch"],
         }
     ]
-    form = WorkspaceCreateForm(repos_with_branches)
-    form.cleaned_data = {
+    data = {
         "name": "test",
         "repo": "http://example.com/derp/test-repo",
         "branch": "unknown-branch",
+        "purpose": "For testing",
     }
+    form = WorkspaceCreateForm(repos_with_branches, data)
 
-    with pytest.raises(ValidationError) as e:
-        form.clean()
-
-    assert e.value.message.startswith("Unknown branch")
+    assert not form.is_valid()
+    assert "branch" in form.errors
 
 
 def test_workspacecreateform_unknown_repo_validation_fails():