diff --git a/Semantic_Analizer_Tests/src/Basic_tests/OopNegativeSemanticTest.ttcn b/Semantic_Analizer_Tests/src/Basic_tests/OopNegativeSemanticTest.ttcn
index 1edb7bd700d20fad8d01e8f22807a329e88fc3dd..86f09659c7a0439f8f993773c7ac85292b9541f1 100755
--- a/Semantic_Analizer_Tests/src/Basic_tests/OopNegativeSemanticTest.ttcn
+++ b/Semantic_Analizer_Tests/src/Basic_tests/OopNegativeSemanticTest.ttcn
@@ -30,6 +30,7 @@ type class BadInheritance extends MyUnion {
 }
 
 type class MinimalClass { }
+type class @trait BaseClass { }
 type class @abstract MinimalAbstractClass { }
 type class @final MinimalFinalClass { }
 type class @trait MinimalTraitClass { }
@@ -46,6 +47,10 @@ type class BadExtends3 extends MinimalFinalClass {
   
 }
 
+type class RepeatedExtends extends MinimalClass, BaseClass, MinimalClass {
+
+}
+
 type class @trait BadTraitClass {
 	public var integer m_int := 0;
 	public timer Timer;
diff --git a/org.eclipse.titan.designer/src/org/eclipse/titan/designer/AST/TTCN3/types/ClassTypeReferenceList.java b/org.eclipse.titan.designer/src/org/eclipse/titan/designer/AST/TTCN3/types/ClassTypeReferenceList.java
index 59adfc1e8cc26d0d0867353f89d8f19ebd5282a9..a5bbfc07d0c5fb4cf1eae24c62eeef1fcfb585ad 100755
--- a/org.eclipse.titan.designer/src/org/eclipse/titan/designer/AST/TTCN3/types/ClassTypeReferenceList.java
+++ b/org.eclipse.titan.designer/src/org/eclipse/titan/designer/AST/TTCN3/types/ClassTypeReferenceList.java
@@ -9,6 +9,7 @@ package org.eclipse.titan.designer.AST.TTCN3.types;
 
 import java.text.MessageFormat;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -36,6 +37,8 @@ public final class ClassTypeReferenceList extends ASTNode implements ILocateable
 	private final String ONLYONNONTRAIT = "A class can only extend one non-trait class";
 	private final String TRAITEXTENDSTRAIT = "A trait class can only extend trait classes";
 	private final String FINALCANNOTBEEXTENDED = "A final class cannot be extended";
+	private final String DUPLICATECOMPONENTREFERENCEFIRST = "Duplicate reference to class `{0}'' was first declared here";
+	private final String DUPLICATECOMPONENTREFERENCEREPEATED = "Duplicate reference to class `{0}'' was declared here again";
 	
 	private Class_Type parentClass;
 	
@@ -144,10 +147,10 @@ public final class ClassTypeReferenceList extends ASTNode implements ILocateable
 				if (classTypeBody != null) {
 					if (classTypeBodies.containsKey(classTypeBody)) {
 						classTypeBodies.get(classTypeBody).getId().getLocation().reportSingularSemanticError(
-								MessageFormat.format(ComponentTypeReferenceList.DUPLICATECOMPONENTREFERENCEFIRST, classTypeBody.getIdentifier()
+								MessageFormat.format(DUPLICATECOMPONENTREFERENCEFIRST, classTypeBody.getIdentifier()
 										.getDisplayName()));
 						reference.getLocation().reportSemanticError(
-								MessageFormat.format(ComponentTypeReferenceList.DUPLICATECOMPONENTREFERENCEREPEATED, reference.getDisplayName()));
+								MessageFormat.format(DUPLICATECOMPONENTREFERENCEREPEATED, reference.getDisplayName()));
 					} else {
 						classTypeBodies.put(classTypeBody, reference);
 						orderedClassTypeBodies.add(classTypeBody);
diff --git a/org.eclipse.titan.regressiontests/src/org/eclipse/titan/regressiontests/designer/statictests/Basic_tests/OOP_Semantic_tests.java b/org.eclipse.titan.regressiontests/src/org/eclipse/titan/regressiontests/designer/statictests/Basic_tests/OOP_Semantic_tests.java
index 174d4580992c43ad8018252a2aa4eba876df86c3..8148839463a1ed4f1fc4a42fac4e5612dab055d5 100755
--- a/org.eclipse.titan.regressiontests/src/org/eclipse/titan/regressiontests/designer/statictests/Basic_tests/OOP_Semantic_tests.java
+++ b/org.eclipse.titan.regressiontests/src/org/eclipse/titan/regressiontests/designer/statictests/Basic_tests/OOP_Semantic_tests.java
@@ -45,10 +45,10 @@ public class OOP_Semantic_tests {
 
 	private ArrayList<MarkerToCheck> oopNegative_ttcn_initializer() {
 		//oopNegativeSemanticTest.ttcn
-		ArrayList<MarkerToCheck> markersToCheck = new ArrayList<MarkerToCheck>(41);
+		ArrayList<MarkerToCheck> markersToCheck = new ArrayList<MarkerToCheck>(44);
 		int lineNum = 28;
 		markersToCheck.add(new MarkerToCheck("class type expected",  lineNum, IMarker.SEVERITY_ERROR));
-		lineNum += 9;
+		lineNum += 10;
 		int i = 0;
 		for (i = 0; i < 2; i++) {
 			markersToCheck.add(new MarkerToCheck("A class can only extend one non-trait class", lineNum, IMarker.SEVERITY_ERROR));
@@ -58,6 +58,10 @@ public class OOP_Semantic_tests {
 		markersToCheck.add(new MarkerToCheck("A trait class can only extend trait classes",  lineNum, IMarker.SEVERITY_ERROR));
 		lineNum += 4;
 		markersToCheck.add(new MarkerToCheck("A final class cannot be extended",  lineNum, IMarker.SEVERITY_ERROR));
+		lineNum += 4;
+		markersToCheck.add(new MarkerToCheck("A class can only extend one non-trait class",  lineNum, IMarker.SEVERITY_ERROR));
+		markersToCheck.add(new MarkerToCheck("Duplicate reference to class `MinimalClass' was declared here again",  lineNum, IMarker.SEVERITY_ERROR));
+		markersToCheck.add(new MarkerToCheck("Duplicate reference to class `MinimalClass' was first declared here",  lineNum, IMarker.SEVERITY_ERROR));
 		lineNum += 5;
 		for (i = 0; i < 2; i++) {
 			markersToCheck.add(new MarkerToCheck("Trait classes can only declare methods", lineNum++, IMarker.SEVERITY_ERROR));