diff --git a/agent/config/builder.go b/agent/config/builder.go
index 9f7c0e005..73c067811 100644
--- a/agent/config/builder.go
+++ b/agent/config/builder.go
@@ -174,6 +174,9 @@ func (b *Builder) ReadPath(path string) error {
 // ReadFile parses a JSON or HCL config file and appends it to the list of
 // config sources.
 func (b *Builder) ReadFile(path string) error {
+	if !strings.HasSuffix(path, ".json") && !strings.HasSuffix(path, ".hcl") {
+		return fmt.Errorf(`Missing or invalid file extension for %q. Please use ".json" or ".hcl".`, path)
+	}
 	data, err := ioutil.ReadFile(path)
 	if err != nil {
 		return fmt.Errorf("config: ReadFile failed on %s: %s", path, err)
diff --git a/command/agent_test.go b/command/agent_test.go
index 431fff7e6..2ab73e35e 100644
--- a/command/agent_test.go
+++ b/command/agent_test.go
@@ -229,11 +229,17 @@ func TestProtectDataDir(t *testing.T) {
 		t.Fatalf("err: %v", err)
 	}
 
-	cfgFile := testutil.TempFile(t, "consul")
-	defer os.Remove(cfgFile.Name())
+	cfgDir := testutil.TempDir(t, "consul-config")
+	defer os.RemoveAll(cfgDir)
+
+	cfgFilePath := filepath.Join(cfgDir, "consul.json")
+	cfgFile, err := os.Create(cfgFilePath)
+	if err != nil {
+		t.Fatalf("Unable to create file %v, got error:%v", cfgFilePath, err)
+	}
 
 	content := fmt.Sprintf(`{"server": true, "bind_addr" : "10.0.0.1", "data_dir": "%s"}`, dir)
-	_, err := cfgFile.Write([]byte(content))
+	_, err = cfgFile.Write([]byte(content))
 	if err != nil {
 		t.Fatalf("err: %v", err)
 	}