diff --git a/pkgs/development/compilers/ecl/default.nix b/pkgs/development/compilers/ecl/default.nix
index c937ad95afa4..644ce3cc6be6 100644
--- a/pkgs/development/compilers/ecl/default.nix
+++ b/pkgs/development/compilers/ecl/default.nix
@@ -59,6 +59,8 @@ stdenv.mkDerivation rec {
   ];
 
   configureFlags = [
+    # Fix build with gcc15
+    "CFLAGS=-std=gnu17"
     (if threadSupport then "--enable-threads" else "--disable-threads")
     "--with-gmp-incdir=${lib.getDev gmp}/include"
     "--with-gmp-libdir=${lib.getLib gmp}/lib"