diff --git a/src/features/vsProvider.ts b/src/features/vsProvider.ts
index 9c6ff2e..5f8e325 100644
--- a/src/features/vsProvider.ts
+++ b/src/features/vsProvider.ts
@@ -62,8 +62,13 @@ export default class ValeServerProvider implements vscode.CodeActionProvider {
   private async runVale(file: vscode.TextDocument) {
     const folder = path.dirname(file.fileName);
 
-    const binaryLocation = utils.readBinaryLocation(file);
-    const configLocation = utils.readFileLocation(file);
+    const binaryLocation = utils.readBinaryLocation(this.logger, file);
+    const configLocation = utils.readFileLocation(this.logger, file);
+    if (binaryLocation == null || configLocation == null) {
+      // `file` is not part of the workspace, so we could not resolve a workspace-relative path. Ignore this file.
+      return;
+    }
+
     // There are two cases we need to handle here:
     //
     // (1) If we're given an explicit value for `--config`, then we should
diff --git a/src/features/vsUtils.ts b/src/features/vsUtils.ts
index 2435d42..c139ad1 100644
--- a/src/features/vsUtils.ts
+++ b/src/features/vsUtils.ts
@@ -6,38 +6,37 @@ import { execFile } from "child_process";
 
 import * as vscode from "vscode";
 
-export const readBinaryLocation = (file: vscode.TextDocument) => {
+// If `customPath` contains `${workspaceFolder}`, replaces it with the workspace that `file` comes from.
+// Return `null` if `customPath` contains `${workspaceFolder}` and `file` is _not_ part of the workspace.
+function replaceWorkspaceFolder(logger: vscode.OutputChannel, customPath: string, file: vscode.TextDocument): string | null {
+  customPath = path.normalize(customPath);
+  const workspaceFolder = vscode.workspace.getWorkspaceFolder(file.uri);
+  if (workspaceFolder) {
+    return customPath.replace(
+      "${workspaceFolder}",
+      workspaceFolder.uri.fsPath
+    );
+  }
+  logger.appendLine(`Not running Vale on file '${file.uri}' as it is not contained within the workspace`);
+  return null;
+}
+
+export const readBinaryLocation = (logger: vscode.OutputChannel, file: vscode.TextDocument): string | null => {
   const configuration = vscode.workspace.getConfiguration();
 
   let customBinaryPath = configuration.get<string>("vale.valeCLI.path");
   if (customBinaryPath) {
-    customBinaryPath = path.normalize(customBinaryPath);
-    const workspaceFolder = vscode.workspace.getWorkspaceFolder(file.uri);
-    if (workspaceFolder) {
-      customBinaryPath = customBinaryPath.replace(
-        "${workspaceFolder}",
-        workspaceFolder.uri.fsPath
-      );
-    }
-    return customBinaryPath;
+    return replaceWorkspaceFolder(logger, customBinaryPath, file);
   }
   return which.sync("vale");
 };
 
-export const readFileLocation = (file: vscode.TextDocument) => {
+export const readFileLocation = (logger: vscode.OutputChannel, file: vscode.TextDocument): string | null => {
   const configuration = vscode.workspace.getConfiguration();
 
   let customConfigPath = configuration.get<string>("vale.valeCLI.config");
   if (customConfigPath) {
-    customConfigPath = path.normalize(customConfigPath);
-    const workspaceFolder = vscode.workspace.getWorkspaceFolder(file.uri);
-    if (workspaceFolder) {
-      customConfigPath = customConfigPath.replace(
-        "${workspaceFolder}",
-        workspaceFolder.uri.fsPath
-      );
-    }
-    return customConfigPath;
+    return replaceWorkspaceFolder(logger, customConfigPath, file);
   }
   return "";
 };