diff --git a/pkgs/development/libraries/opal/default.nix b/pkgs/development/libraries/opal/default.nix
index c79c3cbe4d62..5090aa874ec4 100644
--- a/pkgs/development/libraries/opal/default.nix
+++ b/pkgs/development/libraries/opal/default.nix
@@ -17,7 +17,7 @@ stdenv.mkDerivation rec {
 
   enableParallelBuilding = true;
 
-  NIX_CFLAGS = "-D__STDC_CONSTANT_MACROS=1";
+  NIX_CFLAGS_COMPILE = "-D__STDC_CONSTANT_MACROS=1";
 
   patches = [ ./disable-samples-ftbfs.diff ./libav9.patch ./libav10.patch ];