diff --git a/pkgs/by-name/ra/raspa/package.nix b/pkgs/by-name/ra/raspa/package.nix
index e8589739f396..be044efb051b 100644
--- a/pkgs/by-name/ra/raspa/package.nix
+++ b/pkgs/by-name/ra/raspa/package.nix
@@ -33,6 +33,9 @@ stdenv.mkDerivation (finalAttrs: {
     openblas
   ];
 
+  # K&R `T func()` declarations whose definitions take real args
+  env.CFLAGS = "-std=gnu17";
+
   # Prepare for the Python binding packaging.
   strictDeps = true;