diff --git a/native/roles/change-roles-header-right-button.react.js b/native/roles/change-roles-header-right-button.react.js
--- a/native/roles/change-roles-header-right-button.react.js
+++ b/native/roles/change-roles-header-right-button.react.js
@@ -10,12 +10,15 @@
   changeThreadMemberRoles,
   changeThreadMemberRolesActionTypes,
 } from 'lib/actions/thread-actions.js';
+import { otherUsersButNoOtherAdmins } from 'lib/selectors/thread-selectors.js';
+import { roleIsAdminRole } from 'lib/shared/thread-utils.js';
 import {
   useDispatchActionPromise,
   useServerCall,
 } from 'lib/utils/action-utils.js';
 
 import type { NavigationRoute } from '../navigation/route-names';
+import { useSelector } from '../redux/redux-utils.js';
 import { useColors } from '../themes/colors.js';
 
 type Props = {
@@ -25,12 +28,17 @@
 function ChangeRolesHeaderRightButton(props: Props): React.Node {
   const { threadInfo, memberInfo, role: selectedRole } = props.route.params;
   const { role: initialRole } = memberInfo;
+  invariant(initialRole, 'Expected initial role to be defined');
   invariant(selectedRole, 'Expected selected role to be defined');
   const navigation = useNavigation();
 
   const callChangeThreadMemberRoles = useServerCall(changeThreadMemberRoles);
   const dispatchActionPromise = useDispatchActionPromise();
 
+  const otherUsersButNoOtherAdminsValue = useSelector(
+    otherUsersButNoOtherAdmins(threadInfo.id),
+  );
+
   const { purpleLink } = useColors();
   const textStyle = React.useMemo(
     () => ({
@@ -46,6 +54,16 @@
       return;
     }
 
+    const memberIsAdmin = roleIsAdminRole(threadInfo.roles[initialRole]);
+
+    if (otherUsersButNoOtherAdminsValue && memberIsAdmin) {
+      navigation.setParams({
+        ...props.route.params,
+        shouldShowError: true,
+      });
+      return;
+    }
+
     const createChangeThreadMemberRolesPromise = () => {
       return callChangeThreadMemberRoles(
         threadInfo.id,
@@ -66,8 +84,11 @@
     initialRole,
     memberInfo.id,
     navigation,
+    otherUsersButNoOtherAdminsValue,
+    props.route.params,
     selectedRole,
     threadInfo.id,
+    threadInfo.roles,
   ]);
 
   return (
diff --git a/native/roles/change-roles-screen.react.js b/native/roles/change-roles-screen.react.js
--- a/native/roles/change-roles-screen.react.js
+++ b/native/roles/change-roles-screen.react.js
@@ -20,6 +20,7 @@
   +threadInfo: ThreadInfo,
   +memberInfo: RelativeMemberInfo,
   +role: ?string,
+  +shouldShowError?: boolean,
 };
 
 type Props = {
@@ -29,7 +30,7 @@
 
 function ChangeRolesScreen(props: Props): React.Node {
   const { navigation } = props;
-  const { threadInfo, memberInfo, role } = props.route.params;
+  const { threadInfo, memberInfo, role, shouldShowError } = props.route.params;
   invariant(role, 'Role must be defined');
 
   const styles = useStyles(unboundStyles);
@@ -65,6 +66,7 @@
         threadInfo,
         memberInfo,
         role: newRole,
+        shouldShowError: false,
       });
     },
     [navigation, setSelectedRole, roleOptions, memberInfo, threadInfo],
@@ -88,7 +90,22 @@
       },
       onRoleChange,
     );
-  }, [roleOptions, onRoleChange, activeTheme, showActionSheetWithOptions]);
+  }, [showActionSheetWithOptions, roleOptions, onRoleChange, activeTheme]);
+
+  const errorMessage = React.useMemo(() => {
+    if (!shouldShowError) {
+      return null;
+    }
+
+    return (
+      <View style={styles.errorMessageContainer}>
+        <Text style={styles.errorMessage}>Cannot change role.</Text>
+        <Text style={styles.errorMessage}>
+          There must be at least one admin at any given time.
+        </Text>
+      </View>
+    );
+  }, [shouldShowError, styles.errorMessage, styles.errorMessageContainer]);
 
   return (
     <View>
@@ -109,6 +126,7 @@
           <SWMansionIcon name="edit-1" size={20} style={styles.pencilIcon} />
         </TouchableOpacity>
       </View>
+      {errorMessage}
     </View>
   );
 }
@@ -158,6 +176,16 @@
   pencilIcon: {
     color: 'panelInputSecondaryForeground',
   },
+  errorMessageContainer: {
+    display: 'flex',
+    flexDirection: 'column',
+    alignItems: 'center',
+    marginTop: 20,
+  },
+  errorMessage: {
+    color: 'redText',
+    fontSize: 16,
+  },
 };
 
 export default ChangeRolesScreen;