diff --git a/aegisub/configure.in b/aegisub/configure.in
index afafce0fa..9213ef108 100644
--- a/aegisub/configure.in
+++ b/aegisub/configure.in
@@ -162,7 +162,7 @@ AS_IF([test -d "$srcdir/.svn"], [
   SVN_REVISION=`cat $srcdir/svn_revision`
   AC_MSG_RESULT([$SVN_REVISION from "$srcdir/svn_revision"])
 ], [test -d "$srcdir/../.git"], [
-  SVN_REVISION=[`git log | grep git-svn-id -m 1 | sed 's/.*@\([0-9]\+\) .*/\1/'`]
+  SVN_REVISION=[`git log | grep git-svn-id -m 1 | sed -E 's/.*@([0-9]+) .*/\1/'`]
   AC_MSG_RESULT([$SVN_REVISION from git])
 ], [
   AC_MSG_RESULT([not found])