3 files changed, 26 insertions, 4 deletions
diff --git a/src/corelib/statemachine/qabstracttransition.cpp b/src/corelib/statemachine/qabstracttransition.cpp
index 1897aa6..c6a261d 100644
--- a/src/corelib/statemachine/qabstracttransition.cpp
+++ b/src/corelib/statemachine/qabstracttransition.cpp
@@ -180,7 +180,7 @@ QAbstractTransition::QAbstractTransition(const QList<QAbstractState*> &targets,
     d_ptr->q_ptr = this;
 #endif
     Q_D(QAbstractTransition);
-    d->targetStates = targets;
+    setTargetStates(targets);
 }
 
 /*!
@@ -221,7 +221,7 @@ QAbstractTransition::QAbstractTransition(QAbstractTransitionPrivate &dd,
     d_ptr->q_ptr = this;
 #endif
     Q_D(QAbstractTransition);
-    d->targetStates = targets;
+    setTargetStates(targets);
 }
 
 /*!
@@ -265,7 +265,7 @@ void QAbstractTransition::setTargetState(QAbstractState* target)
     if (!target)
         d->targetStates.clear();
     else
-        d->targetStates = QList<QAbstractState*>() << target;
+        setTargetStates(QList<QAbstractState*>() << target);
 }
 
 /*!
@@ -284,6 +284,15 @@ QList<QAbstractState*> QAbstractTransition::targetStates() const
 void QAbstractTransition::setTargetStates(const QList<QAbstractState*> &targets)
 {
     Q_D(QAbstractTransition);
+
+    for (int i=0; i<targets.size(); ++i) {
+        QAbstractState *target = targets.at(i);
+        if (target->machine() != 0 && target->machine()->rootState() == target) {
+            qWarning("QAbstractTransition::setTargetStates: root state cannot be target of transition");
+            return;
+        }
+    }
+
     d->targetStates = targets;
 }
 
diff --git a/src/corelib/statemachine/qstate.cpp b/src/corelib/statemachine/qstate.cpp
index 4c9e033..acee27d 100644
--- a/src/corelib/statemachine/qstate.cpp
+++ b/src/corelib/statemachine/qstate.cpp
@@ -280,11 +280,15 @@ QAbstractState *QState::errorState() const
 void QState::setErrorState(QAbstractState *state)
 {
     Q_D(QState);
-    if (state != 0 && QAbstractStatePrivate::get(state)->machine() != d->machine()) {
+    if (state != 0 && state->machine() != machine()) {
         qWarning("QState::setErrorState: error state cannot belong "
                  "to a different state machine");
         return;
     }
+    if (state->machine() != 0 && state->machine()->rootState() == state) {
+        qWarning("QStateMachine::setErrorState: root state cannot be error state");
+        return;
+    }
 
     d->errorState = state;
 }
@@ -301,6 +305,13 @@ QAbstractTransition *QState::addTransition(QAbstractTransition *transition)
         qWarning("QState::addTransition: cannot add null transition");
         return 0;
     }
+
+    // machine() will always be non-null for root state
+    if (machine() != 0 && machine()->rootState() == this) {
+        qWarning("QState::addTransition: cannot add transition from root state");
+        return 0;
+    }
+
     const QList<QAbstractState*> &targets = QAbstractTransitionPrivate::get(transition)->targetStates;
     for (int i = 0; i < targets.size(); ++i) {
         QAbstractState *t = targets.at(i);
diff --git a/src/corelib/statemachine/qstatemachine.cpp b/src/corelib/statemachine/qstatemachine.cpp
index 21e564c..110a4f8 100644
--- a/src/corelib/statemachine/qstatemachine.cpp
+++ b/src/corelib/statemachine/qstatemachine.cpp
@@ -1011,6 +1011,8 @@ void QStateMachinePrivate::setError(QStateMachine::Error errorCode, QAbstractSta
     }
 
     Q_ASSERT(currentErrorState != 0);
+    Q_ASSERT(currentErrorState != rootState);
+    
     QState *lca = findLCA(QList<QAbstractState*>() << currentErrorState << currentContext);
     addStatesToEnter(currentErrorState, lca, pendingErrorStates, pendingErrorStatesForDefaultEntry);
 }