diff --git a/config/validate/rules.go b/config/validate/rules.go
index 416e6ec..f8397dc 100644
--- a/config/validate/rules.go
+++ b/config/validate/rules.go
@@ -34,6 +34,7 @@ var Rules []rule = []rule{
 	checkStructure,
 	checkValidity,
 	checkWriteFiles,
+	checkWriteFilesUnderCoreos,
 }
 
 // checkDiscoveryUrl verifies that the string is a valid url.
@@ -150,3 +151,12 @@ func checkWriteFiles(cfg node, report *Report) {
 		}
 	}
 }
+
+// checkWriteFilesUnderCoreos checks to see if the 'write_files' node is a
+// child of 'coreos' (it shouldn't be).
+func checkWriteFilesUnderCoreos(cfg node, report *Report) {
+	c := cfg.Child("coreos").Child("write_files")
+	if c.IsValid() {
+		report.Info(c.line, "write_files doesn't belong under coreos")
+	}
+}
diff --git a/config/validate/rules_test.go b/config/validate/rules_test.go
index c767dff..d37c181 100644
--- a/config/validate/rules_test.go
+++ b/config/validate/rules_test.go
@@ -319,3 +319,37 @@ func TestCheckWriteFiles(t *testing.T) {
 		}
 	}
 }
+
+func TestCheckWriteFilesUnderCoreos(t *testing.T) {
+	tests := []struct {
+		config string
+
+		entries []Entry
+	}{
+		{},
+		{
+			config: "write_files:\n  - path: /hi",
+		},
+		{
+			config:  "coreos:\n  write_files:\n    - path: /hi",
+			entries: []Entry{{entryInfo, "write_files doesn't belong under coreos", 2}},
+		},
+		{
+			config:  "coreos:\n  write-files:\n    - path: /hyphen",
+			entries: []Entry{{entryInfo, "write_files doesn't belong under coreos", 2}},
+		},
+	}
+
+	for i, tt := range tests {
+		r := Report{}
+		n, err := parseCloudConfig([]byte(tt.config), &r)
+		if err != nil {
+			panic(err)
+		}
+		checkWriteFilesUnderCoreos(n, &r)
+
+		if e := r.Entries(); !reflect.DeepEqual(tt.entries, e) {
+			t.Errorf("bad report (%d, %q): want %#v, got %#v", i, tt.config, tt.entries, e)
+		}
+	}
+}