diff --git a/include/core/SkMatrix.h b/include/core/SkMatrix.h
index 9dd4fc9..741c349 100644
--- a/include/core/SkMatrix.h
+++ b/include/core/SkMatrix.h
@@ -400,6 +400,10 @@
         return memcmp(a.fMat, b.fMat, sizeof(a.fMat)) != 0;
     }
 
+    enum {
+        // flatten/unflatten will never return a value larger than this
+        kMaxFlattenSize = 9 * sizeof(SkScalar) + sizeof(uint32_t)
+    };
     // return the number of bytes written, whether or not buffer is null
     uint32_t flatten(void* buffer) const;
     // return the number of bytes read
diff --git a/src/effects/SkGroupShape.cpp b/src/effects/SkGroupShape.cpp
index 0e7640f..b8edc82 100644
--- a/src/effects/SkGroupShape.cpp
+++ b/src/effects/SkGroupShape.cpp
@@ -80,8 +80,6 @@
     return CreateProc;
 }
 
-#define SAFE_MATRIX_STORAGE_SIZE    (sizeof(SkMatrix)*2)
-
 void SkGroupShape::flatten(SkFlattenableWriteBuffer& buffer) {
     this->INHERITED::flatten(buffer);
 
@@ -92,7 +90,7 @@
     while (rec < stop) {
         buffer.writeFlattenable(rec->fShape);
         if (rec->fMatrixRef) {
-            char storage[SAFE_MATRIX_STORAGE_SIZE];
+            char storage[SkMatrix::kMaxFlattenSize];
             uint32_t size = rec->fMatrixRef->flatten(storage);
             buffer.write32(size);
             buffer.writePad(storage, size);
@@ -110,8 +108,7 @@
         SkMatrixRef* mr = NULL;
         uint32_t size = buffer.readS32();
         if (size) {
-            char storage[SAFE_MATRIX_STORAGE_SIZE];
-            SkASSERT(size <= SAFE_MATRIX_STORAGE_SIZE);
+            char storage[SkMatrix::kMaxFlattenSize];
             buffer.read(storage, SkAlign4(size));
             mr = SkNEW(SkMatrixRef);
             mr->unflatten(storage);
diff --git a/tests/MatrixTest.cpp b/tests/MatrixTest.cpp
index 68e587b..052687d 100644
--- a/tests/MatrixTest.cpp
+++ b/tests/MatrixTest.cpp
@@ -27,6 +27,25 @@
     return nearly_equal(m, identity);
 }
 
+static void test_flatten(skiatest::Reporter* reporter, const SkMatrix& m) {
+    // add 100 in case we have a bug, I don't want to kill my stack in the test
+    char buffer[SkMatrix::kMaxFlattenSize + 100];
+    uint32_t size1 = m.flatten(NULL);
+    uint32_t size2 = m.flatten(buffer);
+    REPORTER_ASSERT(reporter, size1 == size2);
+    REPORTER_ASSERT(reporter, size1 <= SkMatrix::kMaxFlattenSize);
+    
+    SkMatrix m2;
+    uint32_t size3 = m2.unflatten(buffer);
+    REPORTER_ASSERT(reporter, size1 == size2);
+    REPORTER_ASSERT(reporter, m == m2);
+    
+    char buffer2[SkMatrix::kMaxFlattenSize + 100];
+    size3 = m2.flatten(buffer2);
+    REPORTER_ASSERT(reporter, size1 == size2);
+    REPORTER_ASSERT(reporter, memcmp(buffer, buffer2, size1) == 0);
+}
+
 void TestMatrix(skiatest::Reporter* reporter) {
     SkMatrix    mat, inverse, iden1, iden2;
 
@@ -40,11 +59,13 @@
     mat.invert(&inverse);
     iden1.setConcat(mat, inverse);
     REPORTER_ASSERT(reporter, is_identity(iden1));
+    test_flatten(reporter, mat);
 
     mat.setScale(SK_Scalar1/2, SK_Scalar1/2);
     mat.invert(&inverse);
     iden1.setConcat(mat, inverse);
     REPORTER_ASSERT(reporter, is_identity(iden1));
+    test_flatten(reporter, mat);
 
     mat.setScale(SkIntToScalar(3), SkIntToScalar(5), SkIntToScalar(20), 0);
     mat.postRotate(SkIntToScalar(25));
@@ -54,6 +75,8 @@
     REPORTER_ASSERT(reporter, is_identity(iden1));
     iden2.setConcat(inverse, mat);
     REPORTER_ASSERT(reporter, is_identity(iden2));
+    test_flatten(reporter, mat);
+    test_flatten(reporter, iden2);
 
     // rectStaysRect test
     {