diff --git a/serialization/aut/src/main/java/net/automatalib/serialization/aut/InternalAUTParser.java b/serialization/aut/src/main/java/net/automatalib/serialization/aut/InternalAUTParser.java
index bb92fc5c72..c37bfea758 100644
--- a/serialization/aut/src/main/java/net/automatalib/serialization/aut/InternalAUTParser.java
+++ b/serialization/aut/src/main/java/net/automatalib/serialization/aut/InternalAUTParser.java
@@ -38,6 +38,7 @@
 class InternalAUTParser {
 
     private int initialState;
+    private int numStates;
     private final Set<String> alphabetSymbols = new HashSet<>();
     private final Map<Integer, Map<String, Integer>> transitionMap = new HashMap<>();
 
@@ -63,9 +64,9 @@ public <I> InputModelData<I, SimpleAutomaton<Integer, I>> parse(Function<String,
             final Map<String, I> inputMap = Maps.asMap(alphabetSymbols, inputTransformer::apply);
             final Alphabet<I> alphabet = Alphabets.fromCollection(inputMap.values());
 
-            final CompactNFA<I> result = new CompactNFA<>(alphabet, transitionMap.size());
+            final CompactNFA<I> result = new CompactNFA<>(alphabet, numStates);
 
-            for (int i = 0; i < transitionMap.size(); i++) {
+            for (int i = 0; i < numStates; i++) {
                 result.addState();
             }
 
@@ -98,9 +99,12 @@ private void parseHeader(BufferedReader reader) throws IOException {
         verifyLBracketAndShift();
         initialState = parseNumberAndShift();
         verifyCommaAndShift();
-        parseNumberAndShift(); // ignore number of states
-        verifyCommaAndShift();
         parseNumberAndShift(); // ignore number of transitions
+        verifyCommaAndShift();
+        numStates = parseNumberAndShift(); // store number of states
+        if (numStates < 1) {
+            throw new IllegalArgumentException("Number of states must be >= 1");
+        }
         verifyRBracketAndShift();
     }
 
@@ -194,6 +198,10 @@ private int parseNumberAndShift() {
             sym = currentLineContent[currentPos];
         }
 
+        if (sb.length() == 0){
+            throw new IllegalArgumentException(buildErrorMessage("Expected a positive number"));
+        }
+
         // forward pointer
         shiftToNextNonWhitespace();
         return Integer.parseInt(sb.toString());
diff --git a/serialization/aut/src/test/java/net/automatalib/serialization/aut/AUTSerializationTest.java b/serialization/aut/src/test/java/net/automatalib/serialization/aut/AUTSerializationTest.java
index 19d951d65c..0f043b5ef1 100644
--- a/serialization/aut/src/test/java/net/automatalib/serialization/aut/AUTSerializationTest.java
+++ b/serialization/aut/src/test/java/net/automatalib/serialization/aut/AUTSerializationTest.java
@@ -34,6 +34,7 @@
 import net.automatalib.util.automata.random.RandomAutomata;
 import net.automatalib.words.Alphabet;
 import net.automatalib.words.impl.Alphabets;
+import net.automatalib.words.impl.ArrayAlphabet;
 import org.testng.Assert;
 import org.testng.annotations.Test;
 
@@ -65,6 +66,28 @@ public void quotationLabelTest() throws Exception {
         }
     }
 
+    @Test
+    public void sinkStateTest() throws Exception {
+        try (InputStream is = AUTSerializationTest.class.getResourceAsStream("/sinkStateTest.aut")) {
+            final SimpleAutomaton<Integer, String> automaton = AUTParser.readAutomaton(is).model;
+            Assert.assertEquals(3, automaton.size());
+
+            final Alphabet<String> alphabet = new ArrayAlphabet<String>("input", "output");
+
+            final Set<Integer> s0 = automaton.getInitialStates();
+            final Set<Integer> t1 = automaton.getSuccessors(s0, Collections.singletonList("input"));
+            final Set<Integer> t2 = automaton.getSuccessors(s0, Collections.singletonList("output"));
+            final Set<Integer> t3 = automaton.getSuccessors(s0, Arrays.asList("input", "output"));
+            final Set<Integer> t4 = automaton.getSuccessors(s0, Arrays.asList("input", "output", "output"));
+
+            Assert.assertEquals(Collections.singleton(0), s0);
+            Assert.assertEquals(Collections.singleton(1), t1);
+            Assert.assertEquals(Collections.singleton(2), t2);
+            Assert.assertEquals(Collections.singleton(0), t3);
+            Assert.assertEquals(Collections.singleton(2), t4);
+        }
+    }
+
     @Test
     public void serializationTest() throws Exception {
         final Alphabet<Integer> alphabet = Alphabets.integers(0, 2);
@@ -92,10 +115,14 @@ private <S, I> void equalityTest(SimpleAutomaton<S, I> src, SimpleAutomaton<S, I
     public void errorTest() throws IOException {
         try (InputStream e1 = AUTSerializationTest.class.getResourceAsStream("/error1.aut");
              InputStream e2 = AUTSerializationTest.class.getResourceAsStream("/error2.aut");
-             InputStream e3 = AUTSerializationTest.class.getResourceAsStream("/error3.aut")) {
+             InputStream e3 = AUTSerializationTest.class.getResourceAsStream("/error3.aut");
+             InputStream e4 = AUTSerializationTest.class.getResourceAsStream("/error4.aut");
+             InputStream e5 = AUTSerializationTest.class.getResourceAsStream("/error5.aut")) {
             Assert.assertThrows(() -> AUTParser.readAutomaton(e1));
             Assert.assertThrows(() -> AUTParser.readAutomaton(e2));
             Assert.assertThrows(() -> AUTParser.readAutomaton(e3));
+            Assert.assertThrows(() -> AUTParser.readAutomaton(e4));
+            Assert.assertThrows(() -> AUTParser.readAutomaton(e5));
         }
     }
 
diff --git a/serialization/aut/src/test/resources/error4.aut b/serialization/aut/src/test/resources/error4.aut
new file mode 100644
index 0000000000..73898677ff
--- /dev/null
+++ b/serialization/aut/src/test/resources/error4.aut
@@ -0,0 +1,4 @@
+des(0, 3, 0)
+(0, a, 1)
+(1, b, 0)
+(1, c, 1)
\ No newline at end of file
diff --git a/serialization/aut/src/test/resources/error5.aut b/serialization/aut/src/test/resources/error5.aut
new file mode 100644
index 0000000000..34be5ec16c
--- /dev/null
+++ b/serialization/aut/src/test/resources/error5.aut
@@ -0,0 +1,2 @@
+des(0, 1, 1)
+(1, z , -2)
\ No newline at end of file
diff --git a/serialization/aut/src/test/resources/sinkStateTest.aut b/serialization/aut/src/test/resources/sinkStateTest.aut
new file mode 100644
index 0000000000..15794c0505
--- /dev/null
+++ b/serialization/aut/src/test/resources/sinkStateTest.aut
@@ -0,0 +1,5 @@
+des(0,4,3)
+(0,input,1)
+(0,output,2)
+(1,input,2)
+(1,output,0)
\ No newline at end of file