diff --git a/pkgs/by-name/ex/exifprobe/package.nix b/pkgs/by-name/ex/exifprobe/package.nix
index b1d5b1cf412c..584eb2abf667 100644
--- a/pkgs/by-name/ex/exifprobe/package.nix
+++ b/pkgs/by-name/ex/exifprobe/package.nix
@@ -15,7 +15,7 @@ stdenv.mkDerivation {
     sha256 = "1c1fhc0v1m452lgnfcijnvrc0by06qfbhn3zkliqi60kv8l2isbp";
   };
 
-  CFLAGS = [ "-O2" ];
+  env.CFLAGS = toString [ "-O2" ];
 
   installFlags = [ "DESTDIR=$(out)" ];