diff --git a/lib/internal/debugger/inspect_repl.js b/lib/internal/debugger/inspect_repl.js
index 4b11023554e268..01e9374e1ceac0 100644
--- a/lib/internal/debugger/inspect_repl.js
+++ b/lib/internal/debugger/inspect_repl.js
@@ -1024,6 +1024,7 @@ function createRepl(inspector) {
       },
 
       watch(expr) {
+        validateString(expr, 'expression');
         ArrayPrototypePush(watchedExpressions, expr);
       },
 
diff --git a/test/sequential/test-debugger-watch-validation.js b/test/sequential/test-debugger-watch-validation.js
new file mode 100644
index 00000000000000..46307c18d55526
--- /dev/null
+++ b/test/sequential/test-debugger-watch-validation.js
@@ -0,0 +1,20 @@
+'use strict';
+const common = require('../common');
+
+common.skipIfInspectorDisabled();
+
+const fixtures = require('../common/fixtures');
+const startCLI = require('../common/debugger');
+
+const assert = require('assert');
+
+const cli = startCLI([fixtures.path('debugger/break.js')]);
+
+(async () => {
+  await cli.waitForInitialBreak();
+  await cli.command('watch()');
+  await cli.waitFor(/ERR_INVALID_ARG_TYPE/);
+  assert.match(cli.output, /TypeError \[ERR_INVALID_ARG_TYPE\]: The "expression" argument must be of type string\. Received undefined/);
+})()
+.finally(() => cli.quit())
+.then(common.mustCall());