diff --git a/autolint.js b/autolint.js
index a756ddd..b94bf3d 100644
--- a/autolint.js
+++ b/autolint.js
@@ -1,6 +1,6 @@
 module.exports = {
     paths: [
-        "lib/*.js",
+        "lib/**/*.js",
         "test/*.js"
     ],
     linterOptions: {
diff --git a/lib/buster-cli/config.js b/lib/buster-cli/config.js
index fbe8482..749c4f6 100644
--- a/lib/buster-cli/config.js
+++ b/lib/buster-cli/config.js
@@ -36,6 +36,37 @@ function noGroupsError(cli, file, groups, options) {
     return new Error(message);
 }
 
+/**
+ * Checks for groups without an environment set.
+ * If such a group is found and it is not extended by at least one other group,
+ * a warning is logged to inform the user, that the group will be ignored.
+ * 
+ * @param {Object[]} groups Groups to check.
+ */
+function checkForEnvSet(groups) {
+
+    var i, j, extended;
+    for (i = 0; i < groups.length; i++) {
+
+        if (!groups[i].environment) {
+
+            extended = false;
+            for (j = 0; j < groups.length && !extended; j++) {
+                if (i !== j && groups[j].config["extends"] === groups[i].name) {
+                    extended = true;
+                }
+            }
+
+            if (!extended) {
+                this.cli.logger.warn("Warning: " +
+                    "no environment set for group \"" +
+                    groups[i].name +
+                    "\", group will be ignored!");
+            }
+        }
+    }
+}
+
 function filterTests(filters, config) {
     var matchers = filters.map(function (filter) {
         return new Minimatch(filter);
@@ -121,8 +152,10 @@ module.exports = Config.prototype = {
                                           " did not match any files"));
             }
             if (files.length === 0) {
-                return callback(new Error(sig + " not provided, and none of\n[" +
-                                          this.defaultFiles.join(", ") + "] exist"));
+                return callback(new Error(sig +
+                    " not provided, and none of\n[" +
+                    this.defaultFiles.join(", ") +
+                    "] exist"));
             }
             try {
                 callback(null, files.map(function (f) {
@@ -152,6 +185,7 @@ module.exports = Config.prototype = {
                     return callback(err);
                 }
                 var groups = config.groups.slice();
+                checkForEnvSet.call(this, groups);
                 this.filter(config, options);
                 var files = emptyFiles(config);
                 if (files.length > 0) {
diff --git a/test/buster-cli-test.js b/test/buster-cli-test.js
index 8fb3117..ed15bc8 100644
--- a/test/buster-cli-test.js
+++ b/test/buster-cli-test.js
@@ -356,7 +356,7 @@ buster.testCase("buster-cli", {
             }.bind(this));
         },
 
-        "configuration with --config": {
+        "with --config": {
             setUp: function () {
                 var json = JSON.stringify({
                     "Node tests": { environment: "node" },
@@ -441,6 +441,66 @@ buster.testCase("buster-cli", {
                     }));
                 }.bind(this));
             }
+
+        },
+
+        "config validation": {
+
+            setUp: function () {
+                sinon.stub(this.cli.logger, "warn");
+            },
+
+            tearDown: cliHelper.clearFixtures,
+
+            "warning for groups without environment set": function (done) {
+
+                var json = JSON.stringify({
+                    "Tests1": {},
+                    "Tests2": {},
+                    "Node tests": { environment: "node" },
+                    "Browser tests": { environment: "browser" }
+                });
+                cliHelper.writeFile("seaman.js", "module.exports = " + json);
+
+                this.cli.parseArgs([], function (errors, options) {
+                    this.cli.loadConfig(options, done(function (err, groups) {
+                        assert.equals(this.cli.logger.warn.callCount, 2);
+                        assert.match(this.cli.logger.warn.args[0], "Warning:");
+                        assert.match(this.cli.logger.warn.args[0],
+                            "no environment set for group \"");
+                        assert.match(this.cli.logger.warn.getCall(0).args[0],
+                            "Tests1");
+                        assert.match(this.cli.logger.warn.getCall(1).args[0],
+                            "Tests2");
+                        assert.match(this.cli.logger.warn.args[0],
+                            "\", group will be ignored!");
+                    }.bind(this)));
+                }.bind(this));
+            },
+
+            "no warning for missing environment if extended": function (done) {
+
+                var json = JSON.stringify({
+                    "Tests1": {},
+                    "Tests2": {},
+                    "Node tests": { environment: "node", "extends": "Tests2" },
+                    "Browser tests": { environment: "browser" }
+                });
+                cliHelper.writeFile("seaman.js", "module.exports = " + json);
+
+                this.cli.parseArgs([], function (errors, options) {
+                    this.cli.loadConfig(options, done(function (err, groups) {
+                        assert.equals(this.cli.logger.warn.callCount, 1);
+                        assert.match(this.cli.logger.warn.args[0], "Warning:");
+                        assert.match(this.cli.logger.warn.args[0],
+                            "no environment set for group \"");
+                        assert.match(this.cli.logger.warn.args[0], "Tests1");
+                        assert.match(this.cli.logger.warn.args[0],
+                            "\", group will be ignored!");
+                    }.bind(this)));
+                }.bind(this));
+            }
+
         },
 
         "config environments": {