diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index 31140a8..429fa5b 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -85,6 +85,9 @@
 
 static constexpr bool kSanityCheckObjects = kIsDebugBuild;
 
+// For b/21333911.
+static constexpr bool kDuplicateClassesCheck = false;
+
 static void ThrowNoClassDefFoundError(const char* fmt, ...)
     __attribute__((__format__(__printf__, 1, 2)))
     SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
@@ -840,6 +843,10 @@
 // the two elements agree on whether their dex file was from an already-loaded oat-file or the
 // new oat file. Any disagreement indicates a collision.
 bool ClassLinker::HasCollisions(const OatFile* oat_file, std::string* error_msg) {
+  if (!kDuplicateClassesCheck) {
+    return false;
+  }
+
   // Dex files are registered late - once a class is actually being loaded. We have to compare
   // against the open oat files. Take the dex_lock_ that protects oat_files_ accesses.
   ReaderMutexLock mu(Thread::Current(), dex_lock_);
diff --git a/test/Android.run-test.mk b/test/Android.run-test.mk
index fa13fe5..3ca1c06 100644
--- a/test/Android.run-test.mk
+++ b/test/Android.run-test.mk
@@ -259,6 +259,11 @@
     $(COMPILER_TYPES),$(RELOCATE_TYPES),$(TRACE_TYPES),$(GC_TYPES),$(JNI_TYPES),$(IMAGE_TYPES), \
     $(PICTEST_TYPES),$(DEBUGGABLE_TYPES),131-structural-change,$(ALL_ADDRESS_SIZES))
 
+# 138-duplicate-classes-check. Turned off temporarily, b/21333911.
+ART_TEST_KNOWN_BROKEN += $(call all-run-test-names,$(TARGET_TYPES),$(RUN_TYPES),$(PREBUILD_TYPES), \
+    $(COMPILER_TYPES),$(RELOCATE_TYPES),$(TRACE_TYPES),$(GC_TYPES),$(JNI_TYPES),$(IMAGE_TYPES), \
+    $(PICTEST_TYPES),$(DEBUGGABLE_TYPES),138-duplicate-classes-check,$(ALL_ADDRESS_SIZES))
+
 # All these tests check that we have sane behavior if we don't have a patchoat or dex2oat.
 # Therefore we shouldn't run them in situations where we actually don't have these since they
 # explicitly test for them. These all also assume we have an image.