diff --git a/libs/binder/Parcel.cpp b/libs/binder/Parcel.cpp
index 777c22a..2c37624 100644
--- a/libs/binder/Parcel.cpp
+++ b/libs/binder/Parcel.cpp
@@ -542,7 +542,7 @@
         return BAD_VALUE;
     }
 
-    if ((mDataSize+len) > mDataCapacity) {
+    if ((mDataPos + len) > mDataCapacity) {
         // grow data
         err = growData(len);
         if (err != NO_ERROR) {
diff --git a/libs/binder/tests/binderParcelUnitTest.cpp b/libs/binder/tests/binderParcelUnitTest.cpp
index 6259d9d..a71da3f 100644
--- a/libs/binder/tests/binderParcelUnitTest.cpp
+++ b/libs/binder/tests/binderParcelUnitTest.cpp
@@ -197,6 +197,17 @@
     ASSERT_EQ(2, p2.readInt32());
 }
 
+TEST(Parcel, AppendWithBadDataPos) {
+    Parcel p1;
+    p1.writeInt32(1);
+    p1.writeInt32(1);
+    Parcel p2;
+    p2.setDataCapacity(8);
+    p2.setDataPosition(10000);
+
+    EXPECT_EQ(android::BAD_VALUE, p2.appendFrom(&p1, 0, 8));
+}
+
 TEST(Parcel, HasBinders) {
     sp<IBinder> b1 = sp<BBinder>::make();