diff --git a/dom0/qvm-core/qubesutils.py b/dom0/qvm-core/qubesutils.py
index 2c77238f..5d65cff6 100644
--- a/dom0/qvm-core/qubesutils.py
+++ b/dom0/qvm-core/qubesutils.py
@@ -70,6 +70,23 @@ def size_to_human (size):
     else:
         return str(round(size/(1024.0*1024*1024),1)) + ' GiB'
 
+def parse_size(size):
+    units = [ ('K', 1024), ('KB', 1024),
+        ('M', 1024*1024), ('MB', 1024*1024),
+        ('G', 1024*1024*1024), ('GB', 1024*1024*1024),
+    ]
+
+    size = size.strip().upper()
+    if size.isdigit():
+        return size
+
+    for unit, multiplier in units:
+        if size.endswith(unit):
+            size = size[:-len(unit)].strip()
+            return int(size)*multiplier
+
+    raise QubesException("Invalid size: {0}.".format(size))
+
 def print_stdout(text):
     print (text)
 
diff --git a/dom0/qvm-tools/qvm-grow-private b/dom0/qvm-tools/qvm-grow-private
index ffa114ae..5e778c1c 100755
--- a/dom0/qvm-tools/qvm-grow-private
+++ b/dom0/qvm-tools/qvm-grow-private
@@ -22,6 +22,7 @@
 
 from qubes.qubes import QubesVmCollection
 from qubes.qubes import QubesException
+from qubesutils import parse_size
 from optparse import OptionParser
 import subprocess
 import os
@@ -30,24 +31,6 @@ import sys
 
 qvm_run_path = "/usr/bin/qvm-run"
 
-def parse_size(size):
-    units = [ ('K', 1024), ('KB', 1024),
-        ('M', 1024*1024), ('MB', 1024*1024),
-        ('G', 1024*1024*1024), ('GB', 1024*1024*1024),
-    ]
-
-    size = size.strip().upper()
-    if size.isdigit():
-        return size
-
-    for unit, multiplier in units:
-        if size.endswith(unit):
-            size = size[:-len(unit)].strip()
-            return int(size)*multiplier
-    
-    print >> sys.stderr, "Invalid size: {0}.".format(size)
-    exit(1)
-
 def main():
     usage = "usage: %prog <vm-name> <size>"
     parser = OptionParser (usage)