diff --git a/src/modules/languages/rust.nix b/src/modules/languages/rust.nix
index 960f81019..fe7920a6b 100644
--- a/src/modules/languages/rust.nix
+++ b/src/modules/languages/rust.nix
@@ -35,7 +35,7 @@ in
       defaultText = lib.literalExpression ''[ ]'';
       description = ''
         List of extra [targets](https://github.com/nix-community/fenix#supported-platforms-and-targets)
-        to install. Defaults to only the native target. 
+        to install. Defaults to only the native target.
       '';
     };
 
@@ -136,8 +136,8 @@ in
               if cfg.toolchain ? rust-src
               then "${cfg.toolchain.rust-src}/lib/rustlib/src/rust/library"
               else pkgs.rustPlatform.rustLibSrc;
-            RUSTFLAGS = "${moldFlags} ${cfg.rustflags}";
-            RUSTDOCFLAGS = "${moldFlags}";
+            RUSTFLAGS = lib.mkIf (moldFlags != "" || cfg.rustflags != "") (lib.concatStringsSep " " (lib.filter (x: x != "") [moldFlags cfg.rustflags]));
+            RUSTDOCFLAGS = lib.mkIf (moldFlags != "") moldFlags;
             CFLAGS = lib.optionalString pkgs.stdenv.isDarwin "-iframework ${config.devenv.profile}/Library/Frameworks";
           };