diff --git a/vdmj/src/main/java/com/fujitsu/vdmj/runtime/Breakpoint.java b/vdmj/src/main/java/com/fujitsu/vdmj/runtime/Breakpoint.java
index 331c269ee..aeda3edeb 100644
--- a/vdmj/src/main/java/com/fujitsu/vdmj/runtime/Breakpoint.java
+++ b/vdmj/src/main/java/com/fujitsu/vdmj/runtime/Breakpoint.java
@@ -82,8 +82,6 @@ public class Breakpoint implements Serializable
 	public static final int SOURCE = 0;		// A file:line source breakpoint
 	public static final int FUNCTION = 1;	// A function or operation name breakpoint
 
-	public static final int USER_CANCEL = 4999;	// Special message for timeouts
-	
 	public Breakpoint(LexLocation location)
 	{
 		this.location = location;
@@ -231,7 +229,7 @@ public void check(LexLocation execl, Context ctxt)
 
 			case TERMINATE:
 				setExecInterrupt(Breakpoint.NONE);
-				throw new ContextException(USER_CANCEL, "Execution cancelled", location, ctxt);
+				ContextException.throwUserCancel(location, ctxt);
 		}
 		
 		ThreadState state = ctxt.threadState;
diff --git a/vdmj/src/main/java/com/fujitsu/vdmj/runtime/ContextException.java b/vdmj/src/main/java/com/fujitsu/vdmj/runtime/ContextException.java
index d42d62d24..0b7e5971c 100644
--- a/vdmj/src/main/java/com/fujitsu/vdmj/runtime/ContextException.java
+++ b/vdmj/src/main/java/com/fujitsu/vdmj/runtime/ContextException.java
@@ -29,7 +29,8 @@
 @SuppressWarnings("serial")
 public class ContextException extends RuntimeException
 {
-	public static final int STACK_OVERFLOW = 4998;
+	private static final int STACK_OVERFLOW	= 4998;
+	private static final int USER_CANCEL	= 4999;
 	
 	public final LexLocation location;
 	public final Context ctxt;
@@ -56,13 +57,23 @@ public String toString()
 		return getMessage();
 	}
 	
+	public static void throwStackOverflow(LexLocation from, Context ctxt) throws ContextException
+	{
+		throw new ContextException(STACK_OVERFLOW, "Stack overflow", from, ctxt);
+	}
+	
 	public boolean isStackOverflow()
 	{
 		return number == STACK_OVERFLOW;
 	}
 	
+	public static void throwUserCancel(LexLocation from, Context ctxt) throws ContextException
+	{
+		throw new ContextException(USER_CANCEL, "Execution cancelled", from, ctxt);
+	}
+	
 	public boolean isUserCancel()
 	{
-		return number == Breakpoint.USER_CANCEL;
+		return number == USER_CANCEL;
 	}
 }
diff --git a/vdmj/src/main/java/com/fujitsu/vdmj/values/FunctionValue.java b/vdmj/src/main/java/com/fujitsu/vdmj/values/FunctionValue.java
index 25b47fba2..05aae0456 100644
--- a/vdmj/src/main/java/com/fujitsu/vdmj/values/FunctionValue.java
+++ b/vdmj/src/main/java/com/fujitsu/vdmj/values/FunctionValue.java
@@ -343,7 +343,8 @@ public Value eval(
 		catch (StackOverflowError e)
 		{
 			clearData();
-			throw new ContextException(ContextException.STACK_OVERFLOW, "Stack overflow", location, ctxt);
+			ContextException.throwStackOverflow(location, ctxt);
+			return null;	// No reached
 		}
 	}
 
@@ -366,7 +367,8 @@ public Value eval(
 		catch (StackOverflowError e)
 		{
 			clearData();
-			throw new ContextException(ContextException.STACK_OVERFLOW, "Stack overflow", location, ctxt);
+			ContextException.throwStackOverflow(location, ctxt);
+			return null;	// No reached
 		}
 	}
 
diff --git a/vdmj/src/main/java/com/fujitsu/vdmj/values/OperationValue.java b/vdmj/src/main/java/com/fujitsu/vdmj/values/OperationValue.java
index a56a79374..9a3163e55 100644
--- a/vdmj/src/main/java/com/fujitsu/vdmj/values/OperationValue.java
+++ b/vdmj/src/main/java/com/fujitsu/vdmj/values/OperationValue.java
@@ -239,7 +239,8 @@ public Value eval(LexLocation from, ValueList argValues, Context ctxt)
 		}
 		catch (StackOverflowError e)
 		{
-			throw new ContextException(ContextException.STACK_OVERFLOW, "Stack overflow", from, ctxt);
+			ContextException.throwStackOverflow(from, ctxt);
+			return null;	// No reached
 		}
 	}