diff --git a/pefile.py b/pefile.py
index f4ae790..1b9b172 100644
--- a/pefile.py
+++ b/pefile.py
@@ -12,7 +12,7 @@
 Lots of packed malware attempt to abuse the format way beyond its standard use.
 To the best of my knowledge most of the abuses are handled gracefully.
 
-Copyright (c) 2005-2011 Ero Carrera <ero.carrera@gmail.com>
+Copyright (c) 2005-2012 Ero Carrera <ero.carrera@gmail.com>
 
 All rights reserved.
 
@@ -2356,11 +2356,15 @@
             section = self.get_section_by_offset(rva)
             file_offset = self.get_offset_from_rva(rva)
             if section is None:
-                # Find the first section starting at a later offset than that specified by 'rva'
-                first_section_after_offset = min([section.PointerToRawData for section in self.sections
-                                                if section.PointerToRawData > file_offset])
-                section = self.get_section_by_offset(first_section_after_offset)
-                safety_boundary = section.PointerToRawData - file_offset
+                safety_boundary = len(self.__data__) - file_offset
+                sections_after_offset = [section.PointerToRawData for section in self.sections
+                                         if section.PointerToRawData > file_offset]
+                if sections_after_offset:
+                    # Find the first section starting at a later offset than that specified by 'rva'
+                    first_section_after_offset = min(sections_after_offset)
+                    section = self.get_section_by_offset(first_section_after_offset)
+                    if section is not None:
+                        safety_boundary = section.PointerToRawData - file_offset
             else:
                 safety_boundary = section.PointerToRawData + len(section.get_data()) - file_offset
 
@@ -3185,6 +3189,8 @@
                                 'Can\'t read unicode string at offset 0x%x' % (ustr_offset))
                             break
 
+                        if var_string is None:
+                            break
 
                         varfileinfo_struct.Var.append(var_struct)
 
@@ -4665,7 +4671,8 @@
                 continue
 
             dword = struct.unpack('I', data[ i*4 : i*4+4 ])[0]
-            checksum = (checksum & 0xffffffff) + dword + (checksum>>32)
+            # Optimized the calculation (thanks to Emmanuel Bourg for pointing it out!)
+            checksum += dword
             if checksum > 2**32:
                 checksum = (checksum & 0xffffffff) + (checksum >> 32)