diff --git a/backend/src/RecoverablePluginError.ts b/backend/src/RecoverablePluginError.ts
index d589f0f0..0a63ed78 100644
--- a/backend/src/RecoverablePluginError.ts
+++ b/backend/src/RecoverablePluginError.ts
@@ -6,6 +6,7 @@ export enum ERRORS {
   INVALID_EMOJI,
   NO_USER_NOTIFICATION_CHANNEL,
   INVALID_USER_NOTIFICATION_CHANNEL,
+  INVALID_USER,
 }
 
 export const RECOVERABLE_PLUGIN_ERROR_MESSAGES = {
@@ -14,6 +15,7 @@ export const RECOVERABLE_PLUGIN_ERROR_MESSAGES = {
   [ERRORS.INVALID_EMOJI]: "Invalid emoji",
   [ERRORS.NO_USER_NOTIFICATION_CHANNEL]: "No user notify channel specified",
   [ERRORS.INVALID_USER_NOTIFICATION_CHANNEL]: "Invalid user notify channel specified",
+  [ERRORS.INVALID_USER]: "Invalid user",
 };
 
 export class RecoverablePluginError extends Error {
diff --git a/backend/src/plugins/Cases/functions/createCaseNote.ts b/backend/src/plugins/Cases/functions/createCaseNote.ts
index ecea600e..e62f3d05 100644
--- a/backend/src/plugins/Cases/functions/createCaseNote.ts
+++ b/backend/src/plugins/Cases/functions/createCaseNote.ts
@@ -12,6 +12,10 @@ export async function createCaseNote(pluginData: PluginData<CasesPluginType>, ar
   }
 
   const mod = await resolveUser(pluginData.client, args.modId);
+  if (!mod) {
+    throw new RecoverablePluginError(ERRORS.INVALID_USER);
+  }
+
   const modName = `${mod.username}#${mod.discriminator}`;
 
   let body = args.body;
diff --git a/backend/src/plugins/ModActions/commands/UnmuteCmd.ts b/backend/src/plugins/ModActions/commands/UnmuteCmd.ts
index 695fef8c..716ce3f1 100644
--- a/backend/src/plugins/ModActions/commands/UnmuteCmd.ts
+++ b/backend/src/plugins/ModActions/commands/UnmuteCmd.ts
@@ -35,6 +35,7 @@ export const UnmuteCmd = modActionsCommand({
   async run({ pluginData, message: msg, args }) {
     const user = await resolveUser(pluginData.client, args.user);
     if (!user) return sendErrorMessage(pluginData, msg.channel, `User not found`);
+
     const memberToUnmute = await resolveMember(pluginData.client, pluginData.guild, user.id);
     const mutesPlugin = pluginData.getPlugin(MutesPlugin);
     const hasMuteRole = memberToUnmute && mutesPlugin.hasMutedRole(memberToUnmute);
diff --git a/backend/src/plugins/ModActions/functions/banUserId.ts b/backend/src/plugins/ModActions/functions/banUserId.ts
index 0f3bfdd2..5d6d615f 100644
--- a/backend/src/plugins/ModActions/functions/banUserId.ts
+++ b/backend/src/plugins/ModActions/functions/banUserId.ts
@@ -20,6 +20,12 @@ export async function banUserId(
 ): Promise<BanResult> {
   const config = pluginData.config.get();
   const user = await resolveUser(pluginData.client, userId);
+  if (!user) {
+    return {
+      status: "failed",
+      error: "Invalid user",
+    };
+  }
 
   // Attempt to message the user *before* banning them, as doing it after may not be possible
   let notifyResult: UserNotificationResult = { method: null, success: true };
diff --git a/backend/src/plugins/Mutes/functions/muteUser.ts b/backend/src/plugins/Mutes/functions/muteUser.ts
index 4989b7ac..46126656 100644
--- a/backend/src/plugins/Mutes/functions/muteUser.ts
+++ b/backend/src/plugins/Mutes/functions/muteUser.ts
@@ -41,6 +41,11 @@ export async function muteUser(
   }
 
   const user = await resolveUser(pluginData.client, userId);
+  if (!user) {
+    lock.unlock();
+    throw new RecoverablePluginError(ERRORS.INVALID_USER);
+  }
+
   const member = await resolveMember(pluginData.client, pluginData.guild, user.id); // Grab the fresh member so we don't have stale role info
   const config = pluginData.config.getMatchingConfig({ member, userId });
 
diff --git a/backend/src/utils.ts b/backend/src/utils.ts
index 3f6c5ef3..af4c96f7 100644
--- a/backend/src/utils.ts
+++ b/backend/src/utils.ts
@@ -972,8 +972,7 @@ export function resolveUserId(bot: Client, value: string) {
   }
 
   // Just a user ID?
-  const idMatch = value.match(/^\d+$/);
-  if (idMatch) {
+  if (isValidSnowflake(value)) {
     return value;
   }
 
@@ -1000,12 +999,12 @@ export async function resolveUser<T>(bot, value) {
     return new UnknownUser();
   }
 
-  // If we have the user cached, return that directly
   const userId = resolveUserId(bot, value);
   if (!userId) {
-    return new UnknownUser({ id: userId });
+    return null;
   }
 
+  // If we have the user cached, return that directly
   if (bot.users.has(userId)) {
     return bot.users.get(userId);
   }