diff --git a/packages/@vue/cli-plugin-unit-mocha/index.js b/packages/@vue/cli-plugin-unit-mocha/index.js
index f41ea0fffa..aa981d6b60 100644
--- a/packages/@vue/cli-plugin-unit-mocha/index.js
+++ b/packages/@vue/cli-plugin-unit-mocha/index.js
@@ -41,7 +41,7 @@ module.exports = api => {
 
     const inspectPos = rawArgv.findIndex(arg => arg.startsWith('--inspect-brk'))
     if (inspectPos !== -1) {
-      nodeArgs = rawArgv.splice(inspectPos, inspectPos + 1)
+      nodeArgs = rawArgv.splice(inspectPos, 1)
     }
     // for @vue/babel-preset-app <= v4.0.0-rc.7
     process.env.VUE_CLI_BABEL_TARGET_NODE = true