diff --git a/test/plantuml-indentation-with-tabs-test.el b/test/plantuml-indentation-with-tabs-test.el
new file mode 100644
index 0000000..52a5c5f
--- /dev/null
+++ b/test/plantuml-indentation-with-tabs-test.el
@@ -0,0 +1,111 @@
+;;; plantuml-indentation-with-tabs-test.el --- PlantUML Mode indentation tests   -*- lexical-binding: t; -*-
+
+;; Author: René Schmelzer, Tobias Marczewski (mtoboid)
+;; Maintainer: Carlo Sciolla (skuro)
+;; URL: https://github.com/skuro/plantuml-mode
+
+;;; Commentary:
+
+;; Test indentation for class diagrams, specifically using tabs.
+
+;;; Code:
+
+(ert-deftest plantuml-test-indentation/tabs/nested-modules ()
+  "Test correct indentation of plantuml class diagram elements.
+These code examples are taken from www.plantuml.com"
+  (plantuml-test-indent-block-with-tabs
+
+   "
+@startuml
+
+'some comment
+package org.example.module1 {
+interface A {
+doStuff(): String
+getList(): List<Integer>
+}
+
+class B {
+-name: String
++getName(): String
+}
+}
+
+package org.example.module2 {
+class C {
+-count: int
++getCount(): int
+}
+}
+
+A <|.. B
+A <|.. C
+
+@enduml
+"
+   "
+@startuml
+
+'some comment
+package org.example.module1 {
+	interface A {
+		doStuff(): String
+		getList(): List<Integer>
+	}
+
+	class B {
+		-name: String
+		+getName(): String
+	}
+}
+
+package org.example.module2 {
+	class C {
+		-count: int
+		+getCount(): int
+	}
+}
+
+A <|.. B
+A <|.. C
+
+@enduml
+"))
+
+
+(ert-deftest plantuml-test-block-indentation/tabs/package-empty ()
+  "Test correct indentation of an empty package block."
+  (plantuml-test-indent-block-with-tabs
+   "
+package APackage ()
+interface Inter
+"
+   "
+package APackage ()
+interface Inter
+"))
+
+
+(ert-deftest platuml-test-block-indentation/tabs/package-interface-nested ()
+  "Test correct indentation of two nested blocks, a package and an interface
+Note: package is used in deployment and object diagrams as well, see there for more tests."
+  (plantuml-test-indent-block-with-tabs
+   "
+package foo {
+interface Bar {
+baz
+}
+}
+"
+   "
+package foo {
+	interface Bar {
+		baz
+	}
+}
+"))
+
+
+(provide 'plantuml-indentation-class-test)
+
+;;; plantuml-indentation-with-tabs-test.el ends here
diff --git a/test/test-helper.el b/test/test-helper.el
index feb3950..c61902a 100644
--- a/test/test-helper.el
+++ b/test/test-helper.el
@@ -66,6 +66,37 @@ Finally, the indented text in the buffer will be compared with AFTER."
     (indent-region (point-min) (point-max))
     (should (equal (buffer-string) after))))
 
+;; FIXME
+;; This function is just a copy of the above plantuml-test-indent-block with
+;; some minor changes to use indentation with tabs. Perhaps merge the two
+;; functions?
+(defun plantuml-test-indent-block-with-tabs (before after)
+  "Helper for the block indentation tests with tabs.
+
+BEFORE is the text block to be inserted into a temporary buffer.
+AFTER is the expected text block after indentation.
+
+The temporary buffer will be put into `plantuml-mode'. The whole buffer
+will be indented with one tab for each level of indentation.
+
+Finally, the indented text in the buffer will be compared with AFTER."
+
+  (with-temp-buffer
+    ;; fix the JAR location prior to mode initialization
+    ;; for some reason, plantuml-mode disregards the setq-local
+    (setq plantuml-jar-path plantuml-test-jar-path)
+    (plantuml-init-once 'jar)
+
+    (insert before)
+    (goto-char (point-min))
+    (plantuml-mode)
+    ;; ensure that plantuml-indent-level is the default value 8
+    (setq indent-tabs-mode t)
+    (setq plantuml-indent-level 8)
+
+    (indent-region (point-min) (point-max))
+    (should (equal (buffer-string) after))))
+
 ;; enable code coverage
 (when (require 'undercover nil t)
   (undercover "plantuml-mode.el"))