diff --git a/pkgs/development/compilers/dotnet/wrapper.nix b/pkgs/development/compilers/dotnet/wrapper.nix
index 855928718009..b81cc38e28df 100644
--- a/pkgs/development/compilers/dotnet/wrapper.nix
+++ b/pkgs/development/compilers/dotnet/wrapper.nix
@@ -115,7 +115,7 @@ stdenvNoCC.mkDerivation (finalAttrs: {
               sdk = finalAttrs.finalPackage;
               built = stdenv.mkDerivation {
                 name = "${sdk.name}-test-${name}";
-                buildInputs = [ sdk ] ++ buildInputs ++ lib.optional usePackageSource sdk.packages;
+                buildInputs = [ sdk ] ++ buildInputs ++ lib.optionals usePackageSource sdk.packages;
                 # make sure ICU works in a sandbox
                 propagatedSandboxProfile = toString sdk.__propagatedSandboxProfile;
                 unpackPhase =