diff --git a/src/google/protobuf/stubs/strutil.cc b/src/google/protobuf/stubs/strutil.cc
index 1d34870..3844fa6 100644
--- a/src/google/protobuf/stubs/strutil.cc
+++ b/src/google/protobuf/stubs/strutil.cc
@@ -1116,10 +1116,12 @@
 }
 
 char* FastInt64ToBufferLeft(int64 i, char* buffer) {
-  uint64 u = i;
+  uint64 u = 0;
   if (i < 0) {
     *buffer++ = '-';
-    u = -i;
+    u -= i;
+  } else {
+    u = i;
   }
   return FastUInt64ToBufferLeft(u, buffer);
 }
diff --git a/src/google/protobuf/text_format.cc b/src/google/protobuf/text_format.cc
index ba0c302..801a8e3 100644
--- a/src/google/protobuf/text_format.cc
+++ b/src/google/protobuf/text_format.cc
@@ -1315,7 +1315,9 @@
     while (size > buffer_size_) {
       // Data exceeds space in the buffer. Write what we can and request a new
       // buffer.
-      memset(buffer_, ' ', buffer_size_);
+      if (buffer_size_ > 0) {
+        memset(buffer_, ' ', buffer_size_);
+      }
       size -= buffer_size_;
       void* void_buffer;
       failed_ = !output_->Next(&void_buffer, &buffer_size_);