diff --git a/src/cryptobox/tests/tools.py b/src/cryptobox/tests/tools.py
index ddb201f..b376604 100644
--- a/src/cryptobox/tests/tools.py
+++ b/src/cryptobox/tests/tools.py
@@ -95,7 +95,8 @@ def prepare_partition(blockdevice):
             stdout = subprocess.PIPE,
             stderr = subprocess.PIPE,
             args = [ '/sbin/sfdisk', blockdevice ])
-        proc.stdin.write(",50,0xC\n,50,L\n")
+        # create two partitions (20MB fat, 20MB ext)
+        proc.stdin.write(",10,0xC\n,10,L\n")
         (output, error) = proc.communicate()
         if proc.returncode != 0:
             raise Exception, "could not partition the device (%s): %s" \