diff --git a/lib/types/AbstractBuilder.js b/lib/types/AbstractBuilder.js
index b7536c003..6361b1135 100644
--- a/lib/types/AbstractBuilder.js
+++ b/lib/types/AbstractBuilder.js
@@ -72,7 +72,8 @@ class AbstractBuilder {
 				throw new Error(`Custom task definition ${taskDef.name} of project ${project.metadata.name} ` +
 					`defines both "beforeTask" and "afterTask" parameters. Only one must be defined.`);
 			}
-			if (!taskDef.beforeTask && !taskDef.afterTask) {
+			if (this.taskExecutionOrder.length && !taskDef.beforeTask && !taskDef.afterTask) {
+				// Iff there are tasks configured, beforeTask or afterTask must be given
 				throw new Error(`Custom task definition ${taskDef.name} of project ${project.metadata.name} ` +
 					`defines neither a "beforeTask" nor an "afterTask" parameter. One must be defined.`);
 			}
@@ -115,17 +116,23 @@ class AbstractBuilder {
 
 			this.tasks[newTaskName] = execTask;
 
-			const refTaskName = taskDef.beforeTask || taskDef.afterTask;
-			let refTaskIdx = this.taskExecutionOrder.indexOf(refTaskName);
-			if (refTaskIdx === -1) {
-				throw new Error(`Could not find task ${refTaskName}, referenced by custom task ${newTaskName}, ` +
-					`to be scheduled for project ${project.metadata.name}`);
-			}
-			if (taskDef.afterTask) {
-				// Insert after index of referenced task
-				refTaskIdx++;
+			if (this.taskExecutionOrder.length) {
+				// There is at least one task configured. Use before- and afterTask to add the custom task
+				const refTaskName = taskDef.beforeTask || taskDef.afterTask;
+				let refTaskIdx = this.taskExecutionOrder.indexOf(refTaskName);
+				if (refTaskIdx === -1) {
+					throw new Error(`Could not find task ${refTaskName}, referenced by custom task ${newTaskName}, ` +
+						`to be scheduled for project ${project.metadata.name}`);
+				}
+				if (taskDef.afterTask) {
+					// Insert after index of referenced task
+					refTaskIdx++;
+				}
+				this.taskExecutionOrder.splice(refTaskIdx, 0, newTaskName);
+			} else {
+				// There is no task configured so far. Just add the custom task
+				this.taskExecutionOrder.push(newTaskName);
 			}
-			this.taskExecutionOrder.splice(refTaskIdx, 0, newTaskName);
 		}
 	}
 
diff --git a/test/lib/types/AbstractBuilder.js b/test/lib/types/AbstractBuilder.js
index 971a78b9a..c656ca89c 100644
--- a/test/lib/types/AbstractBuilder.js
+++ b/test/lib/types/AbstractBuilder.js
@@ -77,6 +77,16 @@ class CustomBuilder extends AbstractBuilder {
 	}
 }
 
+class EmptyBuilder extends AbstractBuilder {
+	constructor({project, resourceCollections}) {
+		super({parentLogger, project, resourceCollections});
+	}
+
+	addStandardTasks({resourceCollections, project}) {
+		// None - like the ModuleBuilder
+	}
+}
+
 test("Instantiation with standard tasks only", (t) => {
 	const project = clone(applicationBTree);
 
@@ -178,6 +188,46 @@ test.serial("Instantiation with custom task", (t) => {
 		"Order of tasks is correct");
 });
 
+test.serial("Instantiation of empty builder with custom tasks", (t) => {
+	const customTask = function() {};
+	sinon.stub(taskRepository, "getTask").returns(customTask);
+
+	const project = clone(applicationBTree);
+	project.builder = {
+		customTasks: [{
+			name: "myTask"
+		}, {
+			name: "myTask2",
+			beforeTask: "myTask"
+		}]
+	};
+	const customBuilder = new EmptyBuilder({project});
+	t.truthy(customBuilder.tasks["myTask"], "Custom task has been added to task array");
+	t.truthy(customBuilder.tasks["myTask2"], "Custom task 2 has been added to task array");
+	t.deepEqual(customBuilder.taskExecutionOrder,
+		["myTask2", "myTask"],
+		"Order of tasks is correct");
+});
+
+test.serial("Instantiation of empty builder with 2nd custom tasks defining neither beforeTask nor afterTask", (t) => {
+	const customTask = function() {};
+	sinon.stub(taskRepository, "getTask").returns(customTask);
+
+	const project = clone(applicationBTree);
+	project.builder = {
+		customTasks: [{
+			name: "myTask"
+		}, {
+			name: "myTask2" // should define before- or afterTask
+		}]
+	};
+	const error = t.throws(() => {
+		new EmptyBuilder({project});
+	}, Error);
+	t.deepEqual(error.message, `Custom task definition myTask2 of project application.b defines ` +
+		`neither a "beforeTask" nor an "afterTask" parameter. One must be defined.`, "Correct exception thrown");
+});
+
 test.serial("Instantiation with custom task defined three times", (t) => {
 	const customTask = function() {};
 	sinon.stub(taskRepository, "getTask").returns(customTask);