diff --git a/lib/config/defaults.js b/lib/config/defaults.js
index a8debf25..c1795b99 100644
--- a/lib/config/defaults.js
+++ b/lib/config/defaults.js
@@ -23,7 +23,6 @@ const defaults = {
   // nodemon.on('stdout/stderr')
   stdout: true,
   watchOptions: {},
-  ext: 'js mjs cjs json',
 };
 
 if ((process.env.NODE_OPTIONS || '').includes('--loader')) {
diff --git a/lib/config/exec.js b/lib/config/exec.js
index 68c2a2de..6d17eabb 100644
--- a/lib/config/exec.js
+++ b/lib/config/exec.js
@@ -27,7 +27,7 @@ function execFromPackage() {
     if (pkg.scripts && pkg.scripts.start) {
       return { exec: pkg.scripts.start };
     }
-  } catch (e) { }
+  } catch (e) {}
 
   return null;
 }
@@ -78,8 +78,10 @@ function exec(nodemonOptions, execMap) {
 
   // if there's no script passed, try to get it from the first argument
   if (!options.script && (options.args || []).length) {
-    script = expandScript(options.args[0],
-      options.ext && ('.' + (options.ext || 'js').split(',')[0]));
+    script = expandScript(
+      options.args[0],
+      options.ext && '.' + (options.ext || 'js').split(',')[0]
+    );
 
     // if the script was found, shift it off our args
     if (script !== options.args[0]) {
@@ -101,8 +103,7 @@ function exec(nodemonOptions, execMap) {
       if (!options.script) {
         options.script = found.script;
       }
-      if (Array.isArray(options.args) &&
-        options.scriptPosition === null) {
+      if (Array.isArray(options.args) && options.scriptPosition === null) {
         options.scriptPosition = options.args.length;
       }
     }
@@ -115,8 +116,8 @@ function exec(nodemonOptions, execMap) {
 
   var extension = options.ext;
   if (extension === undefined) {
-    var isJS = scriptExt === 'js' || scriptExt === 'mjs';
-    extension = (isJS || !scriptExt) ? 'js,mjs' : scriptExt;
+    var isJS = scriptExt === 'js' || scriptExt === 'mjs' || scriptExt === 'cjs';
+    extension = isJS || !scriptExt ? 'js,mjs,cjs' : scriptExt;
     extension += ',json'; // Always watch JSON files
   }
 
@@ -147,8 +148,10 @@ function exec(nodemonOptions, execMap) {
     });
 
     var newExec = substitution(options.exec);
-    if (newExec !== options.exec &&
-      options.exec.indexOf('{{filename}}') !== -1) {
+    if (
+      newExec !== options.exec &&
+      options.exec.indexOf('{{filename}}') !== -1
+    ) {
       options.script = null;
     }
     options.exec = newExec;
@@ -160,14 +163,16 @@ function exec(nodemonOptions, execMap) {
     }
   }
 
-
   if (options.exec === 'node' && options.nodeArgs && options.nodeArgs.length) {
     options.execArgs = options.execArgs.concat(options.nodeArgs);
   }
 
   // note: indexOf('coffee') handles both .coffee and .litcoffee
-  if (!execDefined && options.exec === 'node' &&
-    scriptExt.indexOf('coffee') !== -1) {
+  if (
+    !execDefined &&
+    options.exec === 'node' &&
+    scriptExt.indexOf('coffee') !== -1
+  ) {
     options.exec = 'coffee';
 
     // we need to get execArgs set before the script
@@ -187,7 +192,9 @@ function exec(nodemonOptions, execMap) {
   if (options.exec === 'coffee') {
     // don't override user specified extension tracking
     if (options.ext === undefined) {
-      if (extension) { extension += ','; }
+      if (extension) {
+        extension += ',';
+      }
       extension += 'coffee,litcoffee';
     }
 
@@ -203,19 +210,21 @@ function exec(nodemonOptions, execMap) {
   // because the terminal will automatically expand the glob against
   // the file system :(
   extension = (extension.match(/[^,*\s]+/g) || [])
-    .map(ext => ext.replace(/^\./, ''))
+    .map((ext) => ext.replace(/^\./, ''))
     .join(',');
 
   options.ext = extension;
 
   if (options.script) {
-    options.script = expandScript(options.script,
-      extension && ('.' + extension.split(',')[0]));
+    options.script = expandScript(
+      options.script,
+      extension && '.' + extension.split(',')[0]
+    );
   }
 
   options.env = {};
   // make sure it's an object (and since we don't have )
-  if (({}).toString.apply(nodemonOptions.env) === '[object Object]') {
+  if ({}.toString.apply(nodemonOptions.env) === '[object Object]') {
     options.env = utils.clone(nodemonOptions.env);
   } else if (nodemonOptions.env !== undefined) {
     throw new Error('nodemon env values must be an object: { PORT: 8000 }');