diff --git a/include/rapidjson/internal/stack.h b/include/rapidjson/internal/stack.h
index 299e651ed..5c5398c35 100644
--- a/include/rapidjson/internal/stack.h
+++ b/include/rapidjson/internal/stack.h
@@ -126,6 +126,7 @@ class Stack {
 
     template<typename T>
     RAPIDJSON_FORCEINLINE T* PushUnsafe(size_t count = 1) {
+        RAPIDJSON_ASSERT(stackTop_);
         RAPIDJSON_ASSERT(stackTop_ + sizeof(T) * count <= stackEnd_);
         T* ret = reinterpret_cast<T*>(stackTop_);
         stackTop_ += sizeof(T) * count;
diff --git a/include/rapidjson/reader.h b/include/rapidjson/reader.h
index 71916c0ae..dbb5e16fa 100644
--- a/include/rapidjson/reader.h
+++ b/include/rapidjson/reader.h
@@ -934,11 +934,13 @@ class GenericReader {
     #else
                 length = static_cast<SizeType>(__builtin_ffs(r) - 1);
     #endif
-                char* q = reinterpret_cast<char*>(os.Push(length));
-                for (size_t i = 0; i < length; i++)
-                    q[i] = p[i];
+                if (length != 0) {
+                    char* q = reinterpret_cast<char*>(os.Push(length));
+                    for (size_t i = 0; i < length; i++)
+                        q[i] = p[i];
 
-                p += length;
+                    p += length;
+                }
                 break;
             }
             _mm_storeu_si128(reinterpret_cast<__m128i *>(os.Push(16)), s);