diff --git a/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_details.test.tsx b/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_details.test.tsx
index c2af813ced3..96b22babdc9 100644
--- a/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_details.test.tsx
+++ b/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_details.test.tsx
@@ -1309,6 +1309,22 @@ describe('AttributeDetails', () => {
             expect(screen.queryByTestId('attributeTypeLockWrap')).not.toBeInTheDocument();
         });
 
+        it('locks adding an external source while a pending Applies-to resource is on the form, so linking cannot silently change the type', async () => {
+            mockLoadedField(makeTemplate({type: 'select', attrs: {display_name: 'Department', options: [{id: 'opt-1', name: 'Engineering'}]}}), [makeLinked('user', 'user-field')]);
+            renderEdit();
+            await waitForForm();
+
+            expect(screen.getByTestId('attributeExternalSourceTrigger')).toBeDisabled();
+            expect(screen.getByTestId('attributeExternalSourceTriggerLockWrap')).toBeInTheDocument();
+
+            await userEvent.click(screen.getByTestId('attributeAppliesToRow-user-toggle'));
+            await userEvent.click(screen.getByTestId('attributeAppliesToRow-user-remove'));
+
+            await waitFor(() => expect(screen.queryByTestId('attributeAppliesToRow-user')).not.toBeInTheDocument());
+            expect(screen.getByTestId('attributeExternalSourceTrigger')).not.toBeDisabled();
+            expect(screen.queryByTestId('attributeExternalSourceTriggerLockWrap')).not.toBeInTheDocument();
+        });
+
         it('locks Name editing while the attribute is currently applied to a resource', async () => {
             mockLoadedField(makeTemplate(), [makeLinked('user', 'user-field')]);
             renderEdit();
diff --git a/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_details.tsx b/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_details.tsx
index 27eab5d1118..1d20ef6bbae 100644
--- a/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_details.tsx
+++ b/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_details.tsx
@@ -1129,6 +1129,7 @@ function AttributeDetails({disabled = false}: Props): JSX.Element {
                                         fieldType={fieldType}
                                         onLink={handleLink}
                                         disabled={saving || disabled}
+                                        disableAdding={typeLockedByAppliesTo}
                                     />
                                 </div>
                             </div>
diff --git a/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_external_source.test.tsx b/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_external_source.test.tsx
index fb7b0678695..ac730b451c9 100644
--- a/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_external_source.test.tsx
+++ b/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_external_source.test.tsx
@@ -43,6 +43,15 @@ describe('AttributeExternalSource', () => {
         expect(screen.getByRole('menuitem', {name: /^SAML/})).toBeInTheDocument();
     });
 
+    it('disables the add-source trigger when disableAdding is set, without disabling an existing chip\'s edit/remove actions', () => {
+        renderComponent({ldapAttr: 'department', disableAdding: true});
+
+        expect(screen.getByTestId('attributeExternalSourceTrigger')).toBeDisabled();
+        expect(screen.getByTestId('attributeExternalSourceTriggerLockWrap')).toBeInTheDocument();
+        expect(screen.getByTestId('attributeExternalSourceChip-ldap-edit')).not.toBeDisabled();
+        expect(screen.getByTestId('attributeExternalSourceChip-ldap-remove')).not.toBeDisabled();
+    });
+
     it('renders a chip for a linked source prefixed by Synced with, and offers only the remaining source', async () => {
         renderComponent({ldapAttr: 'department'});
 
diff --git a/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_external_source.tsx b/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_external_source.tsx
index 3db10c1fabb..8dfdc15a7c2 100644
--- a/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_external_source.tsx
+++ b/webapp/channels/src/components/admin_console/global_attributes/attribute_details/attribute_external_source.tsx
@@ -9,6 +9,7 @@ import {components} from 'react-select';
 
 import {PencilOutlineIcon, RefreshIcon, SyncIcon} from '@mattermost/compass-icons/components';
 import {buttonClassNames} from '@mattermost/shared/components/button';
+import {WithTooltip} from '@mattermost/shared/components/tooltip';
 
 import {openModal} from 'actions/views/modals';
 
@@ -34,13 +35,21 @@ type Props = {
     fieldType: AttributeFieldType;
     onLink: (source: ExternalSource, value: string) => void;
     disabled?: boolean;
+
+    // Linking a new source forces fieldType to 'text' (see attribute_details.tsx's
+    // handleLink) -- while this attribute is applied to a resource, that would
+    // change its type out from under the server's type_change_with_dependents
+    // guard the same way the Type menu itself is locked for. Only gates the
+    // "add" trigger below: editing or removing an already-linked source never
+    // touches fieldType, so those stay enabled.
+    disableAdding?: boolean;
 };
 
 function sourceValue(source: ExternalSource, ldapAttr: string, samlAttr: string): string {
     return source === 'ldap' ? ldapAttr : samlAttr;
 }
 
-function AttributeExternalSource({ldapAttr, samlAttr, fieldType, onLink, disabled = false}: Props): JSX.Element {
+function AttributeExternalSource({ldapAttr, samlAttr, fieldType, onLink, disabled = false, disableAdding = false}: Props): JSX.Element {
     const {formatMessage} = useIntl();
     const dispatch = useDispatch();
 
@@ -156,41 +165,52 @@ function AttributeExternalSource({ldapAttr, samlAttr, fieldType, onLink, disable
                 </div>
             )}
             {unlinkedSources.length > 0 && (
-                <Menu.Container
-                    menuButton={{
-                        id: TRIGGER_ID,
-                        class: classNames(buttonClassNames({emphasis: 'quaternary'}), 'AttributeExternalSource__trigger'),
-                        disabled,
-                        onMouseDown: handleTriggerMouseDown,
-                        children: (
-                            <>
-                                <RefreshIcon size={16}/>
-                                <FormattedMessage {...messages.triggerLabel}/>
-                                <i className='icon icon-chevron-down'/>
-                            </>
-                        ),
-                        dataTestId: 'attributeExternalSourceTrigger',
-                    }}
-                    menu={{
-                        id: 'attribute-external-source-menu',
-                        'aria-label': formatMessage(messages.triggerLabel),
-                    }}
-                >
-                    {unlinkedSources.map((source) => (
-                        <Menu.Item
-                            id={`attribute-external-source-${source}`}
-                            key={source}
-                            leadingElement={<SyncIcon size={18}/>}
-                            onClick={() => openLinkModal(source)}
-                            labels={(
-                                <>
-                                    <FormattedMessage {...sourceMessages[source].title}/>
-                                    <FormattedMessage {...sourceMessages[source].subtitle}/>
-                                </>
-                            )}
-                        />
-                    ))}
-                </Menu.Container>
+                (() => {
+                    const trigger = (
+                        <Menu.Container
+                            menuButton={{
+                                id: TRIGGER_ID,
+                                class: classNames(buttonClassNames({emphasis: 'quaternary'}), 'AttributeExternalSource__trigger'),
+                                disabled: disabled || disableAdding,
+                                onMouseDown: handleTriggerMouseDown,
+                                children: (
+                                    <>
+                                        <RefreshIcon size={16}/>
+                                        <FormattedMessage {...messages.triggerLabel}/>
+                                        <i className='icon icon-chevron-down'/>
+                                    </>
+                                ),
+                                dataTestId: 'attributeExternalSourceTrigger',
+                            }}
+                            menu={{
+                                id: 'attribute-external-source-menu',
+                                'aria-label': formatMessage(messages.triggerLabel),
+                            }}
+                        >
+                            {unlinkedSources.map((source) => (
+                                <Menu.Item
+                                    id={`attribute-external-source-${source}`}
+                                    key={source}
+                                    leadingElement={<SyncIcon size={18}/>}
+                                    onClick={() => openLinkModal(source)}
+                                    labels={(
+                                        <>
+                                            <FormattedMessage {...sourceMessages[source].title}/>
+                                            <FormattedMessage {...sourceMessages[source].subtitle}/>
+                                        </>
+                                    )}
+                                />
+                            ))}
+                        </Menu.Container>
+                    );
+                    return disableAdding ? (
+                        <WithTooltip title={formatMessage(messages.disabledWhileAppliesToTooltip)}>
+                            <span data-testid='attributeExternalSourceTriggerLockWrap'>
+                                {trigger}
+                            </span>
+                        </WithTooltip>
+                    ) : trigger;
+                })()
             )}
             <span
                 role='status'
@@ -263,6 +283,10 @@ const messages = defineMessages({
         id: 'admin.global_attributes.attribute_details.external_source.links_removed',
         defaultMessage: '{count, plural, one {External source link removed} other {External source links removed}}',
     },
+    disabledWhileAppliesToTooltip: {
+        id: 'admin.global_attributes.attribute_details.external_source.disabled_applies_to_tooltip',
+        defaultMessage: 'Cannot link an external source while this attribute applies to a resource.',
+    },
 });
 
 const sourceMessages = {
diff --git a/webapp/channels/src/i18n/en.json b/webapp/channels/src/i18n/en.json
index 24b4217d370..a723bfd7778 100644
--- a/webapp/channels/src/i18n/en.json
+++ b/webapp/channels/src/i18n/en.json
@@ -1468,6 +1468,7 @@
   "admin.global_attributes.attribute_details.display_name.placeholder": "Add a display name",
   "admin.global_attributes.attribute_details.edit_title": "Edit attribute",
   "admin.global_attributes.attribute_details.external_source.chip_label": "{source}: {value}",
+  "admin.global_attributes.attribute_details.external_source.disabled_applies_to_tooltip": "Cannot link an external source while this attribute applies to a resource.",
   "admin.global_attributes.attribute_details.external_source.edit_link": "Edit {source} link",
   "admin.global_attributes.attribute_details.external_source.ldap.help_text": "The attribute in your AD/LDAP directory to sync this value from.",
   "admin.global_attributes.attribute_details.external_source.ldap.modal_title": "Link to AD/LDAP",