2 files changed, 4 insertions, 5 deletions
diff --git a/pkgs/servers/mail/opensmtpd/extras.nix b/pkgs/servers/mail/opensmtpd/extras.nix
index f7ed6382a7b..5a5fc537d6e 100644
--- a/pkgs/servers/mail/opensmtpd/extras.nix
+++ b/pkgs/servers/mail/opensmtpd/extras.nix
@@ -76,11 +76,10 @@ stdenv.mkDerivation rec {
     "--with-table-redis"
   ];
 
-  NIX_CFLAGS_COMPILE =
-    stdenv.lib.optional enableRedis
+  NIX_CFLAGS_COMPILE = stdenv.lib.optionalString enableRedis
       "-I${hiredis}/include/hiredis -lhiredis"
-    ++ stdenv.lib.optional enableMysql
-      "-L${libmysqlclient}/lib/mysql";
+    + stdenv.lib.optionalString enableMysql
+      " -L${libmysqlclient}/lib/mysql";
 
   meta = with stdenv.lib; {
     homepage = https://www.opensmtpd.org/;
diff --git a/pkgs/servers/mail/postfix/default.nix b/pkgs/servers/mail/postfix/default.nix
index b3345f9420c..c0e6252a551 100644
--- a/pkgs/servers/mail/postfix/default.nix
+++ b/pkgs/servers/mail/postfix/default.nix
@@ -79,7 +79,7 @@ in stdenv.mkDerivation rec {
     make makefiles CCARGS='${ccargs}' AUXLIBS='${auxlibs}'
   '';
 
-  NIX_LDFLAGS = lib.optional withLDAP "-llber";
+  NIX_LDFLAGS = lib.optionalString withLDAP "-llber";
 
   installTargets = [ "non-interactive-package" ];