diff --git a/src/allmydata/scripts/tahoe_add_alias.py b/src/allmydata/scripts/tahoe_add_alias.py
index b7ebcddd5..37c04e9f5 100644
--- a/src/allmydata/scripts/tahoe_add_alias.py
+++ b/src/allmydata/scripts/tahoe_add_alias.py
@@ -5,6 +5,24 @@ from allmydata.scripts.common_http import do_http, check_http_error
 from allmydata.scripts.common import get_aliases
 from allmydata.util.fileutil import move_into_place
 
+def add_line_to_aliasfile(aliasfile, alias, cap):
+    # we use os.path.exists, rather than catching EnvironmentError, to avoid
+    # clobbering the valuable alias file in case of spurious or transient
+    # filesystem errors.
+    if os.path.exists(aliasfile):
+        f = open(aliasfile, "r")
+        aliases = f.read()
+        f.close()
+        if not aliases.endswith("\n"):
+            aliases += "\n"
+    else:
+        aliases = ""
+    aliases += "%s: %s\n" % (alias, cap)
+    f = open(aliasfile+".tmp", "w")
+    f.write(aliases)
+    f.close()
+    move_into_place(aliasfile+".tmp", aliasfile)
+
 def add_alias(options):
     nodedir = options['node-directory']
     alias = options.alias
@@ -21,22 +39,7 @@ def add_alias(options):
     aliasfile = os.path.join(nodedir, "private", "aliases")
     cap = uri.from_string_dirnode(cap).to_string()
 
-    # we use os.path.exists, rather than catching EnvironmentError, to avoid
-    # clobbering the valuable alias file in case of spurious or transient
-    # filesystem errors.
-    if os.path.exists(aliasfile):
-        f = open(aliasfile, "r")
-        aliases = f.read()
-        f.close()
-        if not aliases.endswith("\n"):
-            aliases += "\n"
-    else:
-        aliases = ""
-    aliases += "%s: %s\n" % (alias, cap)
-    f = open(aliasfile+".tmp", "w")
-    f.write(aliases)
-    f.close()
-    move_into_place(aliasfile+".tmp", aliasfile)
+    add_line_to_aliasfile(aliasfile, alias, cap)
 
     print >>stdout, "Alias '%s' added" % (alias,)
     return 0
@@ -69,20 +72,7 @@ def create_alias(options):
 
     # probably check for others..
 
-    # see above about EnvironmentError
-    if os.path.exists(aliasfile):
-        f = open(aliasfile, "r")
-        aliases = f.read()
-        f.close()
-        if not aliases.endswith("\n"):
-            aliases += "\n"
-    else:
-        aliases = ""
-    aliases += "%s: %s\n" % (alias, new_uri)
-    f = open(aliasfile+".tmp", "w")
-    f.write(aliases)
-    f.close()
-    move_into_place(aliasfile+".tmp", aliasfile)
+    add_line_to_aliasfile(aliasfile, alias, new_uri)
 
     print >>stdout, "Alias '%s' created" % (alias,)
     return 0