diff --git a/libutils/Android.bp b/libutils/Android.bp
index 2b98fef..2b7412b 100644
--- a/libutils/Android.bp
+++ b/libutils/Android.bp
@@ -45,6 +45,7 @@
         "StopWatch.cpp",
         "String8.cpp",
         "String16.cpp",
+        "StrongPointer.cpp",
         "SystemClock.cpp",
         "Threads.cpp",
         "Timers.cpp",
diff --git a/libutils/StrongPointer.cpp b/libutils/StrongPointer.cpp
new file mode 100644
index 0000000..ba52502
--- /dev/null
+++ b/libutils/StrongPointer.cpp
@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define LOG_TAG "sp"
+
+#include <log/log.h>
+
+namespace android {
+
+void sp_report_race() { LOG_ALWAYS_FATAL("sp<> assignment detected data race"); }
+}
diff --git a/libutils/include/utils/StrongPointer.h b/libutils/include/utils/StrongPointer.h
index 294e6b6..c2f7722 100644
--- a/libutils/include/utils/StrongPointer.h
+++ b/libutils/include/utils/StrongPointer.h
@@ -108,6 +108,9 @@
     T* m_ptr;
 };
 
+// For code size reasons, we do not want this inlined or templated.
+void sp_report_race();
+
 #undef COMPARE
 
 // ---------------------------------------------------------------------------
@@ -161,19 +164,21 @@
 
 template<typename T>
 sp<T>& sp<T>::operator =(const sp<T>& other) {
+    // Force m_ptr to be read twice, to heuristically check for data races.
+    T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
     T* otherPtr(other.m_ptr);
-    if (otherPtr)
-        otherPtr->incStrong(this);
-    if (m_ptr)
-        m_ptr->decStrong(this);
+    if (otherPtr) otherPtr->incStrong(this);
+    if (oldPtr) oldPtr->decStrong(this);
+    if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
     m_ptr = otherPtr;
     return *this;
 }
 
 template<typename T>
 sp<T>& sp<T>::operator =(sp<T>&& other) {
-    if (m_ptr)
-        m_ptr->decStrong(this);
+    T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
+    if (oldPtr) oldPtr->decStrong(this);
+    if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
     m_ptr = other.m_ptr;
     other.m_ptr = nullptr;
     return *this;
@@ -181,29 +186,30 @@
 
 template<typename T>
 sp<T>& sp<T>::operator =(T* other) {
-    if (other)
-        other->incStrong(this);
-    if (m_ptr)
-        m_ptr->decStrong(this);
+    T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
+    if (other) other->incStrong(this);
+    if (oldPtr) oldPtr->decStrong(this);
+    if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
     m_ptr = other;
     return *this;
 }
 
 template<typename T> template<typename U>
 sp<T>& sp<T>::operator =(const sp<U>& other) {
+    T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
     T* otherPtr(other.m_ptr);
-    if (otherPtr)
-        otherPtr->incStrong(this);
-    if (m_ptr)
-        m_ptr->decStrong(this);
+    if (otherPtr) otherPtr->incStrong(this);
+    if (oldPtr) oldPtr->decStrong(this);
+    if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
     m_ptr = otherPtr;
     return *this;
 }
 
 template<typename T> template<typename U>
 sp<T>& sp<T>::operator =(sp<U>&& other) {
-    if (m_ptr)
-        m_ptr->decStrong(this);
+    T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
+    if (m_ptr) m_ptr->decStrong(this);
+    if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
     m_ptr = other.m_ptr;
     other.m_ptr = nullptr;
     return *this;
@@ -211,10 +217,10 @@
 
 template<typename T> template<typename U>
 sp<T>& sp<T>::operator =(U* other) {
-    if (other)
-        (static_cast<T*>(other))->incStrong(this);
-    if (m_ptr)
-        m_ptr->decStrong(this);
+    T* oldPtr(*const_cast<T* volatile*>(&m_ptr));
+    if (other) (static_cast<T*>(other))->incStrong(this);
+    if (oldPtr) oldPtr->decStrong(this);
+    if (oldPtr != *const_cast<T* volatile*>(&m_ptr)) sp_report_race();
     m_ptr = other;
     return *this;
 }