diff --git a/backend/app/schemas/auth.py b/backend/app/schemas/auth.py
index 79dfc15..bd77b97 100644
--- a/backend/app/schemas/auth.py
+++ b/backend/app/schemas/auth.py
@@ -180,6 +180,8 @@ class ProfileUpdate(BaseModel):
         if v is None:
             return v
         import re
+        if ' ' in v:
+            raise ValueError('Umbral name must be a single word with no spaces')
         if not re.match(r'^[a-zA-Z0-9_-]{3,50}$', v):
             raise ValueError('Umbral name must be 3-50 alphanumeric characters, hyphens, or underscores')
         return v
diff --git a/frontend/src/components/settings/SettingsPage.tsx b/frontend/src/components/settings/SettingsPage.tsx
index 607de0b..dda8c69 100644
--- a/frontend/src/components/settings/SettingsPage.tsx
+++ b/frontend/src/components/settings/SettingsPage.tsx
@@ -227,6 +227,10 @@ export default function SettingsPage() {
 
     // Client-side umbral name validation
     if (field === 'umbral_name') {
+      if (current.includes(' ')) {
+        setUmbralNameError('Must be a single word with no spaces');
+        return;
+      }
       if (!current || !/^[a-zA-Z0-9_-]{3,50}$/.test(current)) {
         setUmbralNameError('3-50 characters: letters, numbers, hyphens, underscores');
         return;