diff --git a/src/main/java/edu/kit/typicalc/model/parser/TypeAssumptionParser.java b/src/main/java/edu/kit/typicalc/model/parser/TypeAssumptionParser.java
index 642553e..53853b8 100644
--- a/src/main/java/edu/kit/typicalc/model/parser/TypeAssumptionParser.java
+++ b/src/main/java/edu/kit/typicalc/model/parser/TypeAssumptionParser.java
@@ -17,6 +17,7 @@ import java.util.regex.Pattern;
  */
 public class TypeAssumptionParser {
 
+    private static final Pattern TYPE_NAME_PATTERN = Pattern.compile("[a-zA-Z][a-zA-Z0-9]*");
     private static final Pattern TYPE_VARIABLE_PATTERN = Pattern.compile("t(\\d+)");
 
     /**
@@ -28,7 +29,11 @@ public class TypeAssumptionParser {
     public Result<Map<VarTerm, TypeAbstraction>, ParseError> parse(Map<String, String> assumptions) {
         Map<VarTerm, TypeAbstraction> typeAssumptions = new LinkedHashMap<>();
         for (Map.Entry<String, String> entry : assumptions.entrySet()) {
-            VarTerm var = new VarTerm(entry.getKey());
+            String typeName = entry.getKey();
+            if (!TYPE_NAME_PATTERN.matcher(typeName).matches()) {
+                return new Result<>(null, ParseError.UNEXPECTED_CHARACTER);
+            }
+            VarTerm var = new VarTerm(typeName);
             Result<TypeAbstraction, ParseError> typeAbs = parseType(entry.getValue());
             if (typeAbs.isError()) {
                 return new Result<>(typeAbs);
diff --git a/src/main/java/edu/kit/typicalc/util/package-info.java b/src/main/java/edu/kit/typicalc/util/package-info.java
index c87488b..1fab186 100644
--- a/src/main/java/edu/kit/typicalc/util/package-info.java
+++ b/src/main/java/edu/kit/typicalc/util/package-info.java
@@ -1,9 +1,4 @@
 /**
  * The util package contains classes used in all components of the application.
  */
-@NonNullFields
-@NonNullApi
-package edu.kit.typicalc.util;
-
-import org.springframework.lang.NonNullApi;
-import org.springframework.lang.NonNullFields;
\ No newline at end of file
+package edu.kit.typicalc.util;
\ No newline at end of file
diff --git a/src/test/java/edu/kit/typicalc/model/parser/TypeAssumptionParserTest.java b/src/test/java/edu/kit/typicalc/model/parser/TypeAssumptionParserTest.java
index 748e782..286f45a 100644
--- a/src/test/java/edu/kit/typicalc/model/parser/TypeAssumptionParserTest.java
+++ b/src/test/java/edu/kit/typicalc/model/parser/TypeAssumptionParserTest.java
@@ -209,6 +209,14 @@ class TypeAssumptionParserTest {
             assertTrue(type.isError());
             assertEquals(entry.getValue(), type.unwrapError());
         }
+        TypeAssumptionParser parser = new TypeAssumptionParser();
+        Result<Map<VarTerm, TypeAbstraction>, ParseError> type = parser.parse(Map.of("föhn", "int"));
+        assertTrue(type.isError());
+        assertEquals(ParseError.UNEXPECTED_CHARACTER, type.unwrapError());
+        parser = new TypeAssumptionParser();
+        type = parser.parse(Map.of("1typ", "int"));
+        assertTrue(type.isError());
+        assertEquals(ParseError.UNEXPECTED_CHARACTER, type.unwrapError());
     }
 
     @Test