diff --git a/pkgs/build-support/fetchgit/default.nix b/pkgs/build-support/fetchgit/default.nix
index f2b4726fef09d..fd267fe34de8a 100644
--- a/pkgs/build-support/fetchgit/default.nix
+++ b/pkgs/build-support/fetchgit/default.nix
@@ -120,6 +120,7 @@ stdenvNoCC.mkDerivation {
 
   passthru = {
     gitRepoUrl = url;
+    inherit tag;
   };
 }
 ))
diff --git a/pkgs/build-support/fetchgithub/default.nix b/pkgs/build-support/fetchgithub/default.nix
index ed24a6239449e..6d580b2e06566 100644
--- a/pkgs/build-support/fetchgithub/default.nix
+++ b/pkgs/build-support/fetchgithub/default.nix
@@ -59,12 +59,14 @@ let
 
   gitRepoUrl = "${baseUrl}.git";
 
+  revWithTag = if tag != null then "refs/tags/${tag}" else rev;
+
   fetcherArgs = (if useFetchGit
     then {
       inherit tag rev deepClone fetchSubmodules sparseCheckout fetchLFS; url = gitRepoUrl;
     } // lib.optionalAttrs (leaveDotGit != null) { inherit leaveDotGit; }
     else {
-      url = "${baseUrl}/archive/${if tag != null then "refs/tags/${tag}" else rev}.tar.gz";
+      url = "${baseUrl}/archive/${revWithTag}.tar.gz";
 
       passthru = {
         inherit gitRepoUrl;
@@ -73,5 +75,5 @@ let
   ) // privateAttrs // passthruAttrs // { inherit name; };
 in
 
-fetcher fetcherArgs // { meta = newMeta; inherit rev owner repo tag; }
+fetcher fetcherArgs // { meta = newMeta; inherit owner repo tag; rev = revWithTag; }
 )
diff --git a/pkgs/build-support/fetchgitlab/default.nix b/pkgs/build-support/fetchgitlab/default.nix
index aef76270d5ec4..c060352d1a9fd 100644
--- a/pkgs/build-support/fetchgitlab/default.nix
+++ b/pkgs/build-support/fetchgitlab/default.nix
@@ -37,10 +37,9 @@ lib.makeOverridable (
         repo
       ]
     );
+    revWithTag = if tag != null then "refs/tags/" + tag else rev;
     escapedSlug = lib.replaceStrings [ "." "/" ] [ "%2E" "%2F" ] slug;
-    escapedRev = lib.replaceStrings [ "+" "%" "/" ] [ "%2B" "%25" "%2F" ] (
-      if tag != null then "refs/tags/" + tag else rev
-    );
+    escapedRevWithTag = lib.replaceStrings [ "+" "%" "/" ] [ "%2B" "%25" "%2F" ] revWithTag;
     passthruAttrs = removeAttrs args [
       "protocol"
       "domain"
@@ -77,7 +76,7 @@ lib.makeOverridable (
           }
         else
           {
-            url = "${protocol}://${domain}/api/v4/projects/${escapedSlug}/repository/archive.tar.gz?sha=${escapedRev}";
+            url = "${protocol}://${domain}/api/v4/projects/${escapedSlug}/repository/archive.tar.gz?sha=${escapedRevWithTag}";
 
             passthru = {
               inherit gitRepoUrl;
@@ -95,9 +94,9 @@ lib.makeOverridable (
     meta.homepage = "${protocol}://${domain}/${slug}/";
     inherit
       tag
-      rev
       owner
       repo
       ;
+    rev = revWithTag;
   }
 )