--- a/hgsubversion/maps.py
+++ b/hgsubversion/maps.py
@@ -1,5 +1,6 @@
 ''' Module for self-contained maps. '''
 
+import errno
 import os
 from mercurial import util as hgutil
 from mercurial import node
@@ -182,7 +183,8 @@ class RevMap(dict):
 
     def __init__(self, repo):
         dict.__init__(self)
-        self.path = os.path.join(repo.path, 'svn', 'rev_map')
+        self.path = self.mappath(repo)
+        self.repo = repo
         self.ypath = os.path.join(repo.path, 'svn', 'lastpulled')
         # TODO(durin42): Consider moving management of the youngest
         # file to svnmeta itself rather than leaving it here.
@@ -212,13 +214,26 @@ class RevMap(dict):
         check = lambda x: x[0][1] == branch and x[0][0] < rev.revnum
         return sorted(filter(check, self.iteritems()), reverse=True)
 
-    def _load(self):
-        f = open(self.path)
+    @staticmethod
+    def mappath(repo):
+        return os.path.join(repo.path, 'svn', 'rev_map')
+
+    @classmethod
+    def readmapfile(cls, repo, missingok=True):
+        try:
+            f = open(cls.mappath(repo))
+        except IOError, err:
+            if not missingok or err.errno != errno.ENOENT:
+                raise
+            return iter([])
         ver = int(f.readline())
-        if ver != self.VERSION:
+        if ver != cls.VERSION:
             print 'revmap too new -- please upgrade'
             raise NotImplementedError
-        for l in f:
+        return f
+
+    def _load(self):
+        for l in self.readmapfile(self.repo):
             revnum, ha, branch = l.split(' ', 2)
             if branch == '\n':
                 branch = None
@@ -230,7 +245,6 @@ class RevMap(dict):
             if revnum < self.oldest or not self.oldest:
                 self.oldest = revnum
             dict.__setitem__(self, (revnum, branch), node.bin(ha))
-        f.close()
 
     def _write(self):
         f = open(self.path, 'w')

--- a/hgsubversion/util.py
+++ b/hgsubversion/util.py
@@ -1,3 +1,4 @@
+import errno
 import re
 import os
 import urllib
@@ -13,6 +14,8 @@ try:
 except ImportError:
     pass
 
+import maps
+
 ignoredfiles = set(['.hgtags', '.hgsvnexternals', '.hgsub', '.hgsubstate'])
 
 b_re = re.compile(r'^\+\+\+ b\/([^\n]*)', re.MULTILINE)
@@ -279,11 +282,17 @@ def revset_fromsvn(repo, subset, x):
     '''
     args = revset.getargs(x, 0, 0, "fromsvn takes no arguments")
 
-    def matches(r):
-        convertinfo = repo[r].extra().get('convert_revision', '')
-        return convertinfo[:4] == 'svn:'
-
-    return [r for r in subset if matches(r)]
+    rev = repo.changelog.rev
+    bin = node.bin
+    try:
+        svnrevs = set(rev(bin(l.split(' ', 2)[1]))
+                      for l in maps.RevMap.readmapfile(repo, missingok=False))
+        return filter(svnrevs.__contains__, subset)
+    except IOError, err:
+        if err.errno != errno.ENOENT:
+            raise
+        raise hgutil.Abort("svn metadata is missing - "
+                           "run 'hg svn rebuildmeta' to reconstruct it")
 
 def revset_svnrev(repo, subset, x):
     '''``svnrev(number)``
@@ -294,17 +303,25 @@ def revset_svnrev(repo, subset, x):
     rev = revset.getstring(args[0],
                            "the argument to svnrev() must be a number")
     try:
-        rev = int(rev)
+        revnum = int(rev)
     except ValueError:
         raise error.ParseError("the argument to svnrev() must be a number")
 
-    def matches(r):
-        convertinfo = repo[r].extra().get('convert_revision', '')
-        if convertinfo[:4] != 'svn:':
-            return False
-        return int(convertinfo[40:].rsplit('@', 1)[-1]) == rev
-
-    return [r for r in subset if matches(r)]
+    rev = rev + ' '
+    revs = []
+    try:
+        for l in maps.RevMap.readmapfile(repo, missingok=False):
+            if l.startswith(rev):
+                n = l.split(' ', 2)[1]
+                r = repo[node.bin(n)].rev()
+                if r in subset:
+                    revs.append(r)
+        return revs
+    except IOError, err:
+        if err.errno != errno.ENOENT:
+            raise
+        raise hgutil.Abort("svn metadata is missing - "
+                           "run 'hg svn rebuildmeta' to reconstruct it")
 
 revsets = {
     'fromsvn': revset_fromsvn,