diff --git a/lib/builder/builder.js b/lib/builder/builder.js
index 9e45cd893..b8a4b0fc1 100644
--- a/lib/builder/builder.js
+++ b/lib/builder/builder.js
@@ -117,8 +117,10 @@ function composeTaskList({dev, selfContained, jsdoc, includedTasks, excludedTask
 			});
 			break;
 		}
-		if (selectedTasks[taskName] !== false) {
+		if (selectedTasks[taskName] === true) {
 			selectedTasks[taskName] = false;
+		} else if (typeof selectedTasks[taskName] === "undefined") {
+			log.warn(`Unable to exclude task '${taskName}': Task is unknown`);
 		}
 	}
 
@@ -133,6 +135,8 @@ function composeTaskList({dev, selfContained, jsdoc, includedTasks, excludedTask
 		}
 		if (selectedTasks[taskName] === false) {
 			selectedTasks[taskName] = true;
+		} else if (typeof selectedTasks[taskName] === "undefined") {
+			log.warn(`Unable to include task '${taskName}': Task is unknown`);
 		}
 	}
 
@@ -403,3 +407,9 @@ module.exports = {
 		}
 	}
 };
+
+// Export local function for testing only
+/* istanbul ignore else */
+if (process.env.NODE_ENV === "test") {
+	module.exports._composeTaskList = composeTaskList;
+}
diff --git a/test/lib/builder/builder-composeTaskList.js b/test/lib/builder/builder-composeTaskList.js
new file mode 100644
index 000000000..44000d95f
--- /dev/null
+++ b/test/lib/builder/builder-composeTaskList.js
@@ -0,0 +1,232 @@
+const test = require("ava");
+const sinon = require("sinon");
+const mock = require("mock-require");
+
+test.beforeEach((t) => {
+	t.context.log = {
+		warn: sinon.stub()
+	};
+	const logger = require("@ui5/logger");
+	sinon.stub(logger, "getGroupLogger").withArgs("builder:builder").returns(t.context.log);
+
+	const builder = mock.reRequire("../../../lib/builder/builder");
+	t.context.composeTaskList = builder._composeTaskList;
+});
+
+test.afterEach.always(() => {
+	sinon.restore();
+	mock.stopAll();
+});
+
+
+[
+	[
+		"composeTaskList: dev=false / selfContained=false / jsdoc=false", {
+			dev: false,
+			selfContained: false,
+			jsdoc: false,
+			includedTasks: [],
+			excludedTasks: []
+		}, [
+			"replaceCopyright",
+			"replaceVersion",
+			"createDebugFiles",
+			"escapeNonAsciiCharacters",
+			"uglify",
+			"buildThemes",
+			"generateLibraryManifest",
+			"generateVersionInfo",
+			"generateFlexChangesBundle",
+			"generateComponentPreload",
+			"generateBundle",
+			"generateLibraryPreload",
+		]
+	],
+	[
+		"composeTaskList: dev=true / selfContained=false / jsdoc=false", {
+			dev: true,
+			selfContained: false,
+			jsdoc: false,
+			includedTasks: [],
+			excludedTasks: []
+		}, [
+			"replaceCopyright",
+			"replaceVersion",
+			"buildThemes"
+		]],
+	[
+		"composeTaskList: dev=false / selfContained=true / jsdoc=false", {
+			dev: false,
+			selfContained: true,
+			jsdoc: false,
+			includedTasks: [],
+			excludedTasks: []
+		}, [
+			"replaceCopyright",
+			"replaceVersion",
+			"createDebugFiles",
+			"escapeNonAsciiCharacters",
+			"uglify",
+			"buildThemes",
+			"transformBootstrapHtml",
+			"generateLibraryManifest",
+			"generateVersionInfo",
+			"generateFlexChangesBundle",
+			"generateStandaloneAppBundle",
+			"generateBundle"
+		]
+	],
+	[
+		"composeTaskList: dev=false / selfContained=false / jsdoc=true", {
+			dev: false,
+			selfContained: false,
+			jsdoc: true,
+			includedTasks: [],
+			excludedTasks: []
+		}, [
+			"escapeNonAsciiCharacters",
+			"executeJsdocSdkTransformation",
+			"generateApiIndex",
+			"generateJsdoc",
+			"buildThemes",
+			"generateVersionInfo",
+			"generateBundle",
+		]
+	],
+	[
+		"composeTaskList: includedTasks / excludedTasks", {
+			dev: false,
+			selfContained: false,
+			jsdoc: false,
+			includedTasks: ["generateResourcesJson", "replaceVersion"],
+			excludedTasks: ["replaceCopyright", "generateApiIndex"]
+		}, [
+			"replaceVersion",
+			"createDebugFiles",
+			"escapeNonAsciiCharacters",
+			"uglify",
+			"buildThemes",
+			"generateLibraryManifest",
+			"generateVersionInfo",
+			"generateFlexChangesBundle",
+			"generateComponentPreload",
+			"generateResourcesJson",
+			"generateBundle",
+			"generateLibraryPreload",
+		]
+	],
+	[
+		"composeTaskList: includedTasks=*", {
+			dev: false,
+			selfContained: false,
+			jsdoc: false,
+			includedTasks: ["*"],
+			excludedTasks: []
+		}, [
+			"replaceCopyright",
+			"replaceVersion",
+			"createDebugFiles",
+			"escapeNonAsciiCharacters",
+			"executeJsdocSdkTransformation",
+			"generateApiIndex",
+			"generateJsdoc",
+			"uglify",
+			"buildThemes",
+			"transformBootstrapHtml",
+			"generateLibraryManifest",
+			"generateVersionInfo",
+			"generateManifestBundle",
+			"generateFlexChangesBundle",
+			"generateComponentPreload",
+			"generateResourcesJson",
+			"generateThemeDesignerResources",
+			"generateStandaloneAppBundle",
+			"generateBundle",
+			"generateLibraryPreload",
+			"generateCachebusterInfo",
+		]
+	],
+	[
+		"composeTaskList: excludedTasks=*", {
+			dev: false,
+			selfContained: false,
+			jsdoc: false,
+			includedTasks: [],
+			excludedTasks: ["*"]
+		}, []
+	],
+	[
+		"composeTaskList: includedTasks with unknown tasks", {
+			dev: false,
+			selfContained: false,
+			jsdoc: false,
+			includedTasks: ["foo", "bar"],
+			excludedTasks: []
+		}, [
+			"replaceCopyright",
+			"replaceVersion",
+			"createDebugFiles",
+			"escapeNonAsciiCharacters",
+			"uglify",
+			"buildThemes",
+			"generateLibraryManifest",
+			"generateVersionInfo",
+			"generateFlexChangesBundle",
+			"generateComponentPreload",
+			"generateBundle",
+			"generateLibraryPreload",
+		], (t) => {
+			const {log} = t.context;
+			t.is(log.warn.callCount, 2);
+			t.deepEqual(log.warn.getCall(0).args, [
+				"Unable to include task 'foo': Task is unknown"
+			]);
+			t.deepEqual(log.warn.getCall(1).args, [
+				"Unable to include task 'bar': Task is unknown"
+			]);
+		}
+	],
+	[
+		"composeTaskList: excludedTasks with unknown tasks", {
+			dev: false,
+			selfContained: false,
+			jsdoc: false,
+			includedTasks: [],
+			excludedTasks: ["foo", "bar"],
+		}, [
+			"replaceCopyright",
+			"replaceVersion",
+			"createDebugFiles",
+			"escapeNonAsciiCharacters",
+			"uglify",
+			"buildThemes",
+			"generateLibraryManifest",
+			"generateVersionInfo",
+			"generateFlexChangesBundle",
+			"generateComponentPreload",
+			"generateBundle",
+			"generateLibraryPreload",
+		], (t) => {
+			const {log} = t.context;
+			t.is(log.warn.callCount, 2);
+			t.deepEqual(log.warn.getCall(0).args, [
+				"Unable to exclude task 'foo': Task is unknown"
+			]);
+			t.deepEqual(log.warn.getCall(1).args, [
+				"Unable to exclude task 'bar': Task is unknown"
+			]);
+		}
+	],
+].forEach(([testTitle, args, expectedTaskList, assertCb]) => {
+	test.serial(testTitle, (t) => {
+		const {composeTaskList, log} = t.context;
+		const taskList = composeTaskList(args);
+		t.deepEqual(taskList, expectedTaskList);
+		if (assertCb) {
+			assertCb(t);
+		} else {
+			// When no cb is defined, no logs are expected
+			t.is(log.warn.callCount, 0);
+		}
+	});
+});