diff --git a/pkgs/build-support/fetchsvn/nix-prefetch-svn b/pkgs/build-support/fetchsvn/nix-prefetch-svn
index b6019386ee91..3e99e6f5de07 100755
--- a/pkgs/build-support/fetchsvn/nix-prefetch-svn
+++ b/pkgs/build-support/fetchsvn/nix-prefetch-svn
@@ -11,6 +11,10 @@ fi
 
 test -n "$rev" || rev="HEAD"
 
+# Use a restrictive umask to ensure that the output in the Nix store
+# is not group- or world-writable.  Nix 0.10 complains about this.
+umask 0022
+
 # Determine the hash, unless it was given.
 if test -z "$hash"; then