diff --git a/base/fs/partitionmaps/gpt.py b/base/fs/partitionmaps/gpt.py
index a798cb4..2502288 100644
--- a/base/fs/partitionmaps/gpt.py
+++ b/base/fs/partitionmaps/gpt.py
@@ -18,6 +18,7 @@ class GPTPartitionMap(AbstractPartitionMap):
 		if bootloader == 'grub':
 			from ..partitions.unformatted import UnformattedPartition
 			self.grub_boot = UnformattedPartition(Bytes('1007KiB'), last_partition())
+			self.grub_boot.offset = gpt_offset
 			self.grub_boot.flags.append('bios_grub')
 			self.partitions.append(self.grub_boot)
 
@@ -28,15 +29,16 @@ class GPTPartitionMap(AbstractPartitionMap):
 		if 'swap' in data:
 			self.swap = GPTSwapPartition(Bytes(data['swap']['size']), last_partition())
 			self.partitions.append(self.swap)
-		self.root = GPTPartition(Bytes(data['root']['size']), data['root']['filesystem'], 'root', last_partition())
+		self.root = GPTPartition(Bytes(data['root']['size']), data['root']['filesystem'],
+		                         'root', last_partition())
 		self.partitions.append(self.root)
 
 		if hasattr(self, 'grub_boot'):
+			self.partitions[1].size -= gpt_offset
 			self.partitions[1].size -= self.grub_boot.size
-
-		# Offset for GPT partitioning table
-		self.partitions[0].offset = gpt_offset
-		self.partitions[0].size -= self.partitions[0].offset
+		else:
+			self.partitions[0].offset = gpt_offset
+			self.partitions[0].size -= gpt_offset
 
 		super(GPTPartitionMap, self).__init__(bootloader)