diff --git a/src/main/java/_12/_1/lukas/FibonacciDynamic.java b/src/main/java/_12/_1/lukas/FibonacciDynamic.java
index 643c0b9..64ebfa0 100644
--- a/src/main/java/_12/_1/lukas/FibonacciDynamic.java
+++ b/src/main/java/_12/_1/lukas/FibonacciDynamic.java
@@ -16,6 +16,9 @@ public class FibonacciDynamic extends Fibonacci {
 
 	@Override
 	public long calculate(int n) {
+		if(n < 0) {
+			throw new IllegalArgumentException("n must not be negative. Negafibonacci numbers are not supported.");
+		}
 		if(memory.containsKey(n)) {
 			return memory.get(n);
 		}
diff --git a/src/main/java/_12/_1/lukas/FibonacciParallelDynamic.java b/src/main/java/_12/_1/lukas/FibonacciParallelDynamic.java
index ca8994b..be2e041 100644
--- a/src/main/java/_12/_1/lukas/FibonacciParallelDynamic.java
+++ b/src/main/java/_12/_1/lukas/FibonacciParallelDynamic.java
@@ -15,6 +15,9 @@ public class FibonacciParallelDynamic extends Fibonacci {
 
 	@Override
 	public long calculate(int n) {
+		if(n < 0) {
+			throw new IllegalArgumentException("n must not be negative. Negafibonacci numbers are not supported.");
+		}
 		if(memory.containsKey(n)) {
 			return memory.get(n);
 		}
diff --git a/src/main/java/_12/_1/lukas/FibonacciParallelRecursive.java b/src/main/java/_12/_1/lukas/FibonacciParallelRecursive.java
index 704034f..0b36ca1 100644
--- a/src/main/java/_12/_1/lukas/FibonacciParallelRecursive.java
+++ b/src/main/java/_12/_1/lukas/FibonacciParallelRecursive.java
@@ -5,6 +5,9 @@ import provided._12._1.Fibonacci;
 public class FibonacciParallelRecursive extends Fibonacci {
 	@Override
 	public long calculate(int n) {
+		if(n < 0) {
+			throw new IllegalArgumentException("n must not be negative. Negafibonacci numbers are not supported.");
+		}
 		if(n == 0 || n == 1) {
 			return n;
 		}
diff --git a/src/main/java/_12/_1/lukas/FibonacciRecursive.java b/src/main/java/_12/_1/lukas/FibonacciRecursive.java
index 2d3c382..7ffd022 100644
--- a/src/main/java/_12/_1/lukas/FibonacciRecursive.java
+++ b/src/main/java/_12/_1/lukas/FibonacciRecursive.java
@@ -5,6 +5,9 @@ import provided._12._1.Fibonacci;
 public class FibonacciRecursive extends Fibonacci {
 	@Override
 	public long calculate(int n) {
+		if(n < 0) {
+			throw new IllegalArgumentException("n must not be negative. Negafibonacci numbers are not supported.");
+		}
 		if(n == 0 || n == 1) {
 			return n;
 		}