diff --git a/pkgs/development/libraries/libagar/libagar_test.nix b/pkgs/development/libraries/libagar/libagar_test.nix
index d4712efd6f1..19efea263c0 100644
--- a/pkgs/development/libraries/libagar/libagar_test.nix
+++ b/pkgs/development/libraries/libagar/libagar_test.nix
@@ -7,6 +7,12 @@ stdenv.mkDerivation {
 
   sourceRoot = "agar-1.5.0/tests";
 
+  # Workaround build failure on -fno-common toolchains:
+  #   ld: textdlg.o:(.bss+0x0): multiple definition of `someString';
+  #     configsettings.o:(.bss+0x0): first defined here
+  # TODO: the workaround can be removed once nixpkgs updates to 1.6.0.
+  NIX_CFLAGS_COMPILE = "-fcommon";
+
   preConfigure = ''
     substituteInPlace configure.in \
       --replace '_BSD_SOURCE' '_DEFAULT_SOURCE'