diff --git a/coderd/workspaces.go b/coderd/workspaces.go
index 1469807b8f6c7..8101772232e1e 100644
--- a/coderd/workspaces.go
+++ b/coderd/workspaces.go
@@ -34,6 +34,17 @@ import (
 
 const workspaceDefaultTTL = 2 * time.Hour
 
+var (
+	ttlMin = time.Minute //nolint:revive // min here means 'minimum' not 'minutes'
+	ttlMax = 7 * 24 * time.Hour
+
+	errTTLMin                  = xerrors.New("time until shutdown must be at least one minute")
+	errTTLMax                  = xerrors.New("time until shutdown must be less than 7 days")
+	errDeadlineTooSoon         = xerrors.New("new deadline must be at least 30 minutes in the future")
+	errDeadlineBeforeStart     = xerrors.New("new deadline must be before workspace start time")
+	errDeadlineOverTemplateMax = xerrors.New("new deadline is greater than template allows")
+)
+
 func (api *API) workspace(rw http.ResponseWriter, r *http.Request) {
 	workspace := httpmw.WorkspaceParam(r)
 	if !api.Authorize(r, rbac.ActionRead, workspace) {
@@ -623,9 +634,11 @@ func (api *API) putExtendWorkspace(rw http.ResponseWriter, r *http.Request) {
 
 		newDeadline := req.Deadline.UTC()
 		if err := validWorkspaceDeadline(job.CompletedAt.Time, newDeadline, time.Duration(template.MaxTtl)); err != nil {
+			// NOTE(Cian): Putting the error in the Message field on request from the FE folks.
+			// Normally, we would put the validation error in Validations, but this endpoint is
+			// not tied to a form or specific named user input on the FE.
 			code = http.StatusBadRequest
-			resp.Message = "Bad extend workspace request."
-			resp.Validations = append(resp.Validations, codersdk.ValidationError{Field: "deadline", Detail: err.Error()})
+			resp.Message = "Cannot extend workspace: " + err.Error()
 			return err
 		}
 
@@ -894,12 +907,12 @@ func validWorkspaceTTLMillis(millis *int64, max time.Duration) (sql.NullInt64, e
 
 	dur := time.Duration(*millis) * time.Millisecond
 	truncated := dur.Truncate(time.Minute)
-	if truncated < time.Minute {
-		return sql.NullInt64{}, xerrors.New("time until shutdown must be at least one minute")
+	if truncated < ttlMin {
+		return sql.NullInt64{}, errTTLMin
 	}
 
-	if truncated > 24*7*time.Hour {
-		return sql.NullInt64{}, xerrors.New("time until shutdown must be less than 7 days")
+	if truncated > ttlMax {
+		return sql.NullInt64{}, errTTLMax
 	}
 
 	if truncated > max {
@@ -915,17 +928,17 @@ func validWorkspaceTTLMillis(millis *int64, max time.Duration) (sql.NullInt64, e
 func validWorkspaceDeadline(startedAt, newDeadline time.Time, max time.Duration) error {
 	soon := time.Now().Add(29 * time.Minute)
 	if newDeadline.Before(soon) {
-		return xerrors.New("new deadline must be at least 30 minutes in the future")
+		return errDeadlineTooSoon
 	}
 
 	// No idea how this could happen.
 	if newDeadline.Before(startedAt) {
-		return xerrors.Errorf("new deadline must be before workspace start time")
+		return errDeadlineBeforeStart
 	}
 
 	delta := newDeadline.Sub(startedAt)
 	if delta > max {
-		return xerrors.New("new deadline is greater than template allows")
+		return errDeadlineOverTemplateMax
 	}
 
 	return nil
diff --git a/coderd/workspaces_test.go b/coderd/workspaces_test.go
index eb275e0f8a0bc..a958c260422e6 100644
--- a/coderd/workspaces_test.go
+++ b/coderd/workspaces_test.go
@@ -1063,14 +1063,15 @@ func TestWorkspaceExtend(t *testing.T) {
 	err = client.PutExtendWorkspace(ctx, workspace.ID, codersdk.PutExtendWorkspaceRequest{
 		Deadline: deadlineTooSoon,
 	})
-	require.ErrorContains(t, err, "new deadline must be at least 30 minutes in the future", "setting a deadline less than 30 minutes in the future should fail")
+	require.ErrorContains(t, err, "unexpected status code 400: Cannot extend workspace: new deadline must be at least 30 minutes in the future", "setting a deadline less than 30 minutes in the future should fail")
 
 	// And with a deadline greater than the template max_ttl should also fail
 	deadlineExceedsMaxTTL := time.Now().Add(time.Duration(template.MaxTTLMillis) * time.Millisecond).Add(time.Minute)
 	err = client.PutExtendWorkspace(ctx, workspace.ID, codersdk.PutExtendWorkspaceRequest{
 		Deadline: deadlineExceedsMaxTTL,
 	})
-	require.ErrorContains(t, err, "new deadline is greater than template allows", "setting a deadline greater than that allowed by the template should fail")
+
+	require.ErrorContains(t, err, "unexpected status code 400: Cannot extend workspace: new deadline is greater than template allows", "setting a deadline greater than that allowed by the template should fail")
 
 	// Updating with a deadline 30 minutes in the future should succeed
 	deadlineJustSoonEnough := time.Now().Add(30 * time.Minute)