diff --git a/infer/src/checkers/ThreadSafety.ml b/infer/src/checkers/ThreadSafety.ml
index 875b3b42d..cd4e952e4 100644
--- a/infer/src/checkers/ThreadSafety.ml
+++ b/infer/src/checkers/ThreadSafety.ml
@@ -37,7 +37,7 @@ module TransferFunctions (CFG : ProcCfg.S) = struct
 
   type lock_model = Lock | Unlock | LockedIfTrue | NoEffect
 
-  type thread_model = MainThread | MainThreadIfTrue | Unknown
+  type thread_model = BackgroundThread | MainThread | MainThreadIfTrue | UnknownThread
 
   type container_access_model = ContainerRead | ContainerWrite
 
@@ -119,20 +119,18 @@ module TransferFunctions (CFG : ProcCfg.S) = struct
        -> NoEffect
 
   let get_thread_model = function
-    | Typ.Procname.Java java_pname
-     -> if is_thread_utils_type java_pname then
-          match Typ.Procname.java_get_method java_pname with
-          | "assertMainThread" | "checkOnMainThread" | "assertOnUiThread"
-           -> MainThread
-          | "isMainThread" | "isUiThread"
-           -> MainThreadIfTrue
-          | _
-           -> Unknown
-        else Unknown
-    (* TODO: we can model this now *)
-    (* Note we are not modelling assertOnNonUiThread or assertOnBackgroundThread. These treated as Unknown *)
+    | Typ.Procname.Java java_pname when is_thread_utils_type java_pname -> (
+      match Typ.Procname.java_get_method java_pname with
+      | "assertMainThread" | "assertOnUiThread" | "checkOnMainThread"
+       -> MainThread
+      | "isMainThread" | "isUiThread"
+       -> MainThreadIfTrue
+      | "assertOnBackgroundThread" | "assertOnNonUiThread" | "checkOnNonUiThread"
+       -> BackgroundThread
+      | _
+       -> UnknownThread )
     | _
-     -> Unknown
+     -> UnknownThread
 
   let get_container_access =
     let is_cpp_container_read =
@@ -608,6 +606,8 @@ module TransferFunctions (CFG : ProcCfg.S) = struct
         let astate = {astate with accesses} in
         let astate =
           match get_thread_model callee_pname with
+          | BackgroundThread
+           -> {astate with threads= ThreadsDomain.Background}
           | MainThread
            -> {astate with threads= ThreadsDomain.Main}
           | MainThreadIfTrue -> (
@@ -622,7 +622,7 @@ module TransferFunctions (CFG : ProcCfg.S) = struct
              -> L.(die InternalError)
                   "Procedure %a specified as returning boolean, but returns nothing"
                   Typ.Procname.pp callee_pname )
-          | Unknown
+          | UnknownThread
            -> astate
         in
         let astate_callee =
diff --git a/infer/tests/codetoanalyze/java/threadsafety/RaceWithMainThread.java b/infer/tests/codetoanalyze/java/threadsafety/RaceWithMainThread.java
index 5fb2b67c7..a07dc97f7 100644
--- a/infer/tests/codetoanalyze/java/threadsafety/RaceWithMainThread.java
+++ b/infer/tests/codetoanalyze/java/threadsafety/RaceWithMainThread.java
@@ -20,6 +20,7 @@ class OurThreadUtils{
 class OurThreadUtil{ /*This is like AndroidThreadUtil*/
   native static boolean isUiThread();
   static void assertOnUiThread(){}
+  static void assertOnBackgroundThread(){}
 }
 
 
@@ -186,4 +187,16 @@ class RaceWithMainThread{
    }
  }
 
+  Object mFld;
+
+  public void confusedAssertBad(boolean b) {
+    if (b) {
+      OurThreadUtil.assertOnBackgroundThread();
+    } else {
+      OurThreadUtil.assertOnUiThread();
+    }
+    // not sure if we're on UI or background, should report
+    mFld = null;
+  }
+
 }
diff --git a/infer/tests/codetoanalyze/java/threadsafety/issues.exp b/infer/tests/codetoanalyze/java/threadsafety/issues.exp
index e12115794..fbbb9c1ef 100644
--- a/infer/tests/codetoanalyze/java/threadsafety/issues.exp
+++ b/infer/tests/codetoanalyze/java/threadsafety/issues.exp
@@ -75,6 +75,7 @@ codetoanalyze/java/threadsafety/Ownership.java, void Ownership.writeToOwnedInCal
 codetoanalyze/java/threadsafety/RaceWithMainThread.java, void RaceWithMainThread.conditional_isMainThread_ElseBranch_Bad(), 7, THREAD_SAFETY_VIOLATION, [access to `codetoanalyze.java.checkers.RaceWithMainThread.ff`]
 codetoanalyze/java/threadsafety/RaceWithMainThread.java, void RaceWithMainThread.conditional_isMainThread_Negation_Bad(), 3, THREAD_SAFETY_VIOLATION, [access to `codetoanalyze.java.checkers.RaceWithMainThread.ff`]
 codetoanalyze/java/threadsafety/RaceWithMainThread.java, void RaceWithMainThread.conditional_isUiThread_ElseBranch_Bad(), 7, THREAD_SAFETY_VIOLATION, [access to `codetoanalyze.java.checkers.RaceWithMainThread.ff`]
+codetoanalyze/java/threadsafety/RaceWithMainThread.java, void RaceWithMainThread.confusedAssertBad(boolean), 7, THREAD_SAFETY_VIOLATION, [access to `codetoanalyze.java.checkers.RaceWithMainThread.mFld`]
 codetoanalyze/java/threadsafety/RaceWithMainThread.java, void RaceWithMainThread.readProtectedUnthreadedBad(), 3, THREAD_SAFETY_VIOLATION, [<Beginning of read trace>,access to `codetoanalyze.java.checkers.RaceWithMainThread.f`,<Beginning of write trace>,access to `codetoanalyze.java.checkers.RaceWithMainThread.f`]
 codetoanalyze/java/threadsafety/RaceWithMainThread.java, void RaceWithMainThread.read_unprotected_unthreaded1_Bad(), 2, THREAD_SAFETY_VIOLATION, [<Beginning of read trace>,access to `codetoanalyze.java.checkers.RaceWithMainThread.f1`,<Beginning of write trace>,access to `codetoanalyze.java.checkers.RaceWithMainThread.f1`]
 codetoanalyze/java/threadsafety/RaceWithMainThread.java, void RaceWithMainThread.read_unprotected_unthreaded_Bad(), 2, THREAD_SAFETY_VIOLATION, [<Beginning of read trace>,access to `codetoanalyze.java.checkers.RaceWithMainThread.f`,<Beginning of write trace>,access to `codetoanalyze.java.checkers.RaceWithMainThread.f`]