diff --git a/pkgs/build-support/fetchdarcs/builder.sh b/pkgs/build-support/fetchdarcs/builder.sh
index ce5537f46f40..75b9066dba6f 100644
--- a/pkgs/build-support/fetchdarcs/builder.sh
+++ b/pkgs/build-support/fetchdarcs/builder.sh
@@ -3,11 +3,15 @@ source $stdenv/setup
 
 tagtext=""
 tagflags=""
-if test -n "$rev"; then
-    tagtext="(tag $rev) "
+# Darcs hashes are sha1 (120 bits, 40-character hex)
+if [[ "$rev" =~ [a-fA-F0-9]{40} ]]; then
+    tagtext="(hash $rev)"
+    tagflags="--to-hash=$rev"
+elif test -n "$rev"; then
+    tagtext="(tag $rev)"
     tagflags="--tag=$rev"
 elif test -n "$context"; then
-    tagtext="(context) "
+    tagtext="(context)"
     tagflags="--context=$context"
 fi
 
diff --git a/pkgs/build-support/fetchdarcs/default.nix b/pkgs/build-support/fetchdarcs/default.nix
index 02777c9900dc..ae38edee4fdf 100644
--- a/pkgs/build-support/fetchdarcs/default.nix
+++ b/pkgs/build-support/fetchdarcs/default.nix
@@ -1,12 +1,17 @@
 {stdenvNoCC, darcs, cacert}:
 
-{url, rev ? null, context ? null, md5 ? "", sha256 ? ""}:
+{ url
+, rev ? null
+, context ? null
+, md5 ? ""
+, sha256 ? ""
+, name ? "fetchdarcs"
+}:
 
 if md5 != "" then
   throw "fetchdarcs does not support md5 anymore, please use sha256"
 else
 stdenvNoCC.mkDerivation {
-  name = "fetchdarcs";
   builder = ./builder.sh;
   nativeBuildInputs = [cacert darcs];
 
@@ -14,5 +19,5 @@ stdenvNoCC.mkDerivation {
   outputHashMode = "recursive";
   outputHash = sha256;
 
-  inherit url rev context;
+  inherit url rev context name;
 }