diff --git a/pkgs/servers/ftp/vsftpd/default.nix b/pkgs/servers/ftp/vsftpd/default.nix
index 1a5bd4370d72..b87d11809b11 100644
--- a/pkgs/servers/ftp/vsftpd/default.nix
+++ b/pkgs/servers/ftp/vsftpd/default.nix
@@ -24,7 +24,11 @@ stdenv.mkDerivation rec {
   '';
 
   NIX_LDFLAGS = "-lcrypt -lssl -lcrypto -lpam -lcap";
-  NIX_CFLAGS_COMPILE = "-Wno-error=enum-conversion";
+
+  # On gcc9, this would produce
+  #   error: '-Werror=enum-conversion': no option -Wenum-conversion
+  NIX_CFLAGS_COMPILE = lib.optionalString (lib.versionAtLeast stdenv.cc.version "10")
+    "-Wno-error=enum-conversion";
 
   enableParallelBuilding = true;