diff --git a/solutions/GuardedSafeToWrite.ql b/solutions/GuardedSafeToWrite.ql
new file mode 100644
index 0000000..3c4a052
--- /dev/null
+++ b/solutions/GuardedSafeToWrite.ql
@@ -0,0 +1,190 @@
+/**
+ * @kind path-problem
+ * @problem.severity warning
+ * @id javascript/example/multiflow
+ */
+
+import javascript
+// XX: debug flow query
+// import semmle.javascript.explore.ForwardDataFlow
+import DataFlow::PathGraph
+import DataFlow as DF
+
+// Flow to consider:
+//
+// var value = this.getParameter('value'); //: source 1
+// var ua = new GR('status');              //: source 2
+// ua.setValue('status',value);            //: taint step
+// ua.update();                            //: sink (if from source 2)
+//
+
+// var value = this.getParameter('value'); //: source 1
+class ParameterSource extends CallExpr {
+  ParameterSource() {
+    exists(Expr inst |
+      this.getCalleeName() = "getParameter" and
+      (this.getReceiver().(ThisExpr) = inst or this.getReceiver().(Identifier) = inst)
+    )
+  }
+}
+
+// ua.setValue('status',value);            //: taint step
+predicate setValueTaintStep(DataFlow::Node pred, DataFlow::Node succ) {
+  exists(DotExpr temp, MethodCallExpr mce, VarAccess gr, VarAccess postgr |
+    temp.getPropertyName() = "setValue" and
+    mce.getReceiver() = temp.getBase() and
+    gr = mce.getReceiver() and
+    pred.asExpr() = mce.getArgument(1) and
+    //
+    // Taint all accesses after setValue call.
+    // Trying data flow, this would be:
+    // succ = gr.flow().getASuccessor+() and
+    //
+    // Using control flow:
+    // 1. without sanitizer
+    gr.getASuccessor+() = postgr and
+    succ.asExpr() = postgr
+    //
+    // 2. with recursive predicate, no sanitizer
+    // recursiveSuccessor(gr, postgr) and
+    // succ.asExpr() = postgr
+    // 3. with recursive predicate, with sanitizer
+    // sanitizerCheckedSuccessor(gr, postgr) and
+    // succ.asExpr() = postgr
+  )
+}
+
+// Def-Use special handling:
+// - Include sanitizer check when flagging successive object member calls in taint
+//   step.
+// - Stop at
+//       ua.safeToWrite()
+predicate sanitizerCheckedSuccessor(ControlFlowNode gr, ControlFlowNode postgr) {
+  gr.getASuccessor() = postgr and
+  not inSafeToWrite(postgr)
+  or
+  exists(ControlFlowNode p |
+    sanitizerCheckedSuccessor(gr, p) and
+    not gr.getASuccessor() = postgr and
+    p.getASuccessor() = postgr
+  )
+  // The final postgr needs to be a VarAccess for this query, but for the
+  // recursion we need to be able to traverse expressions.
+}
+
+predicate foo(VarAccess gr, VarAccess postgr) {
+  exists(DotExpr temp, MethodCallExpr mce |
+    temp.getPropertyName() = "setValue" and
+    mce.getReceiver() = temp.getBase() and
+    gr = mce.getReceiver() and
+    gr.getASuccessor+() = postgr
+  )
+}
+
+predicate foo1(Expr gr, Expr postgr) {
+  exists(DotExpr temp, MethodCallExpr mce |
+    temp.getPropertyName() = "setValue" and
+    mce.getReceiver() = temp.getBase() and
+    gr = mce.getReceiver() and
+    recursiveSuccessor(gr, postgr)
+  )
+}
+
+predicate foo2(Expr gr, Expr postgr) {
+  exists(DotExpr temp, MethodCallExpr mce |
+    temp.getPropertyName() = "setValue" and
+    mce.getReceiver() = temp.getBase() and
+    gr = mce.getReceiver() and
+    sanitizerCheckedSuccessor(gr, postgr)
+  )
+}
+
+predicate inSafeToWrite(ControlFlowNode p) {
+  exists(
+    //  DotExpr temp, MethodCallExpr mce,
+    IfStmt if_
+  |
+    // XX:
+    if_.getAChild+().getFirstControlFlowNode() = p
+    // and
+    // temp.getPropertyName() = "safeToWrite" and
+    // p = mce.getReceiver() and
+    // p = temp.getBase()
+  )
+}
+
+// Preparation for including a sanitizer check when flagging successive object
+// member calls in taint step
+predicate recursiveSuccessor(ControlFlowNode gr, ControlFlowNode postgr) {
+  gr.getASuccessor() = postgr
+  or
+  exists(ControlFlowNode p |
+    recursiveSuccessor(gr, p) and
+    p.getASuccessor() = postgr
+  )
+  // The final postgr needs to be a VarAccess for this query, but for the
+  // recursion we need to be able to traverse expressions.
+}
+
+// source 2 to sink flow
+DF::SourceNode grType(DF::TypeTracker t) {
+  t.start() and
+  exists(GR gr | result.asExpr() = gr)
+  or
+  exists(DF::TypeTracker t2 | result = grType(t2).track(t2, t))
+}
+
+DF::SourceNode grType() { result = grType(DF::TypeTracker::end()) }
+
+// ua.update();                            //: sink (if from source 2)
+DotExpr updateExpression() { result.getPropertyName() = "update" }
+
+VarRef recordUpdate() { result = updateExpression().getBase() }
+
+// var ua = new GR('status');     //: source 2
+class GR extends NewExpr {
+  GR() { this.getCalleeName() = "GR" }
+}
+
+// The global flow configuration
+class FromRequestToGrUpdate extends TaintTracking::Configuration {
+  FromRequestToGrUpdate() { this = "FromRequestToGrUpdate" }
+
+  override predicate isSource(DataFlow::Node source) {
+    exists(ParameterSource getParameter | source.asExpr() = getParameter)
+  }
+
+  override predicate isAdditionalTaintStep(DataFlow::Node pred, DataFlow::Node succ) {
+    setValueTaintStep(pred, succ)
+  }
+
+  override predicate isSanitizerGuard(TaintTracking::SanitizerGuardNode nd) {
+    nd instanceof CanWriteGuard
+  }
+
+  override predicate isSink(DataFlow::Node sink) {
+    exists(VarRef grUpdate |
+      sink.asExpr() = recordUpdate() and
+      grUpdate = sink.asExpr() and
+      grUpdate.getName() = "ua" and
+      // It's only a sink if it connects to source 2
+      grUpdate.flow().getALocalSource() = grType()
+    )
+  }
+}
+
+class CanWriteGuard extends TaintTracking::SanitizerGuardNode, DataFlow::CallNode {
+  CanWriteGuard() { this.getCalleeName() = "safeToWrite" }
+
+  override predicate sanitizes(boolean outcome, Expr e) {
+    // outcome is the result of the conditional (the true or false branch)
+    outcome = true and
+    e = this.getReceiver().asExpr()
+    // or e.getASuccessor+() = this.getReceiver().asExpr()
+  }
+}
+
+from FromRequestToGrUpdate dataflow, DataFlow::PathNode source, DataFlow::PathNode sink
+where dataflow.hasFlowPath(source, sink)
+select sink, source, sink, "Data flow from $@ to $@.", source, source.toString(), sink,
+  sink.toString()
diff --git a/tests/GuardedSafeToWrite/GuardedSafeToWrite.expected b/tests/GuardedSafeToWrite/GuardedSafeToWrite.expected
new file mode 100644
index 0000000..e9660f6
--- /dev/null
+++ b/tests/GuardedSafeToWrite/GuardedSafeToWrite.expected
@@ -0,0 +1,32 @@
+WARNING: Unused predicate foo (/Users/hohn/local/codeql-javascript-multiflow/solutions/GuardedSafeToWrite.ql:75,11-14)
+WARNING: Unused predicate foo1 (/Users/hohn/local/codeql-javascript-multiflow/solutions/GuardedSafeToWrite.ql:84,11-15)
+WARNING: Unused predicate foo2 (/Users/hohn/local/codeql-javascript-multiflow/solutions/GuardedSafeToWrite.ql:93,11-15)
+nodes
+| sample-utility-0.js:5:13:5:46 | value |
+| sample-utility-0.js:5:21:5:46 | this.ge ... value') |
+| sample-utility-0.js:5:21:5:46 | this.ge ... value') |
+| sample-utility-0.js:17:34:17:38 | value |
+| sample-utility-0.js:18:13:18:14 | ua |
+| sample-utility-0.js:18:13:18:14 | ua |
+| sample-utility-1.js:2:9:2:42 | value |
+| sample-utility-1.js:2:17:2:42 | this.ge ... value') |
+| sample-utility-1.js:2:17:2:42 | this.ge ... value') |
+| sample-utility-1.js:14:23:14:27 | value |
+| sample-utility-1.js:15:2:15:3 | ua |
+| sample-utility-1.js:15:2:15:3 | ua |
+edges
+| sample-utility-0.js:5:13:5:46 | value | sample-utility-0.js:17:34:17:38 | value |
+| sample-utility-0.js:5:21:5:46 | this.ge ... value') | sample-utility-0.js:5:13:5:46 | value |
+| sample-utility-0.js:5:21:5:46 | this.ge ... value') | sample-utility-0.js:5:13:5:46 | value |
+| sample-utility-0.js:17:34:17:38 | value | sample-utility-0.js:17:34:17:38 | value |
+| sample-utility-0.js:17:34:17:38 | value | sample-utility-0.js:18:13:18:14 | ua |
+| sample-utility-0.js:17:34:17:38 | value | sample-utility-0.js:18:13:18:14 | ua |
+| sample-utility-1.js:2:9:2:42 | value | sample-utility-1.js:14:23:14:27 | value |
+| sample-utility-1.js:2:17:2:42 | this.ge ... value') | sample-utility-1.js:2:9:2:42 | value |
+| sample-utility-1.js:2:17:2:42 | this.ge ... value') | sample-utility-1.js:2:9:2:42 | value |
+| sample-utility-1.js:14:23:14:27 | value | sample-utility-1.js:14:23:14:27 | value |
+| sample-utility-1.js:14:23:14:27 | value | sample-utility-1.js:15:2:15:3 | ua |
+| sample-utility-1.js:14:23:14:27 | value | sample-utility-1.js:15:2:15:3 | ua |
+#select
+| sample-utility-0.js:18:13:18:14 | ua | sample-utility-0.js:5:21:5:46 | this.ge ... value') | sample-utility-0.js:18:13:18:14 | ua | Data flow from $@ to $@. | sample-utility-0.js:5:21:5:46 | this.ge ... value') | this.ge ... value') | sample-utility-0.js:18:13:18:14 | ua | ua |
+| sample-utility-1.js:15:2:15:3 | ua | sample-utility-1.js:2:17:2:42 | this.ge ... value') | sample-utility-1.js:15:2:15:3 | ua | Data flow from $@ to $@. | sample-utility-1.js:2:17:2:42 | this.ge ... value') | this.ge ... value') | sample-utility-1.js:15:2:15:3 | ua | ua |
diff --git a/tests/GuardedSafeToWrite/GuardedSafeToWrite.qlref b/tests/GuardedSafeToWrite/GuardedSafeToWrite.qlref
new file mode 100644
index 0000000..615ea1b
--- /dev/null
+++ b/tests/GuardedSafeToWrite/GuardedSafeToWrite.qlref
@@ -0,0 +1 @@
+GuardedSafeToWrite.ql
diff --git a/tests/GuardedSafeToWrite/sample-utility-0.js b/tests/GuardedSafeToWrite/sample-utility-0.js
new file mode 100644
index 0000000..4549868
--- /dev/null
+++ b/tests/GuardedSafeToWrite/sample-utility-0.js
@@ -0,0 +1,29 @@
+var SampleUtility = function(){};
+SampleUtility.prototype = Object.extendsObject(Processor, {
+    
+    setUserStatus: function() {
+        var value = this.getParameter('value');
+
+        var ua = new GR('users');
+        ua.query();
+        
+        if(!ua.hasNext()){
+            ua.initialize();
+            ua.setValue('status',value);
+            ua.insert();
+        }
+        else {
+            ua.next();
+            ua.setValue('status',value); // unsafe
+            ua.update();
+        }
+
+        if (ua.safeToWrite()) {
+            ua.setValue('status', value); // safe
+            ua.update();
+        }        
+
+    },
+    
+    type: 'SampleUtility'
+});
diff --git a/tests/GuardedSafeToWrite/sample-utility-1.js b/tests/GuardedSafeToWrite/sample-utility-1.js
new file mode 100644
index 0000000..aea3135
--- /dev/null
+++ b/tests/GuardedSafeToWrite/sample-utility-1.js
@@ -0,0 +1,17 @@
+var SampleUtility = function() {
+    var value = this.getParameter('value');
+
+    var ua = new GR('users');
+    ua.query();
+    
+    if(!ua.hasNext()){
+	ua.initialize();
+	ua.setValue('status',value);
+	ua.insert();
+    }
+    else {
+	ua.next();
+	ua.setValue('status',value);
+	ua.update();
+    }
+}