diff --git a/pkgs/tools/networking/sipsak/default.nix b/pkgs/tools/networking/sipsak/default.nix
index a55a32c21a9..668dc18f8ac 100644
--- a/pkgs/tools/networking/sipsak/default.nix
+++ b/pkgs/tools/networking/sipsak/default.nix
@@ -10,7 +10,11 @@ stdenv.mkDerivation rec {
     c-ares
   ];
 
-  NIX_CFLAGS_COMPILE = "--std=gnu89";
+  # -fcommon: workaround build failure on -fno-common toolchains like upstream
+  # gcc-10. Otherwise build fails as:
+  #   ld: transport.o:/build/source/sipsak.h:323: multiple definition of
+  #     `address'; auth.o:/build/source/sipsak.h:323: first defined here
+  NIX_CFLAGS_COMPILE = "-std=gnu89 -fcommon";
 
   src = fetchFromGitHub {
     owner = "sipwise";