diff --git a/pkgs/development/compilers/ghc/8.4.3.nix b/pkgs/development/compilers/ghc/8.4.3.nix
index 0fecb1d2962..385c33c22ef 100644
--- a/pkgs/development/compilers/ghc/8.4.3.nix
+++ b/pkgs/development/compilers/ghc/8.4.3.nix
@@ -15,7 +15,7 @@
 
 , # If enabled, GHC will be built with the GPL-free but slower integer-simple
   # library instead of the faster but GPLed integer-gmp library.
-  enableIntegerSimple ? false, gmp ? null
+  enableIntegerSimple ? !(gmp.meta.available or false), gmp
 
 , # If enabled, use -fPIC when compiling static libs.
   enableRelocatedStaticLibs ? targetPlatform != hostPlatform
@@ -32,8 +32,6 @@
   ghcFlavour ? stdenv.lib.optionalString (targetPlatform != hostPlatform) "perf-cross"
 }:
 
-assert !enableIntegerSimple -> gmp != null;
-
 let
   inherit (bootPkgs) ghc;
 
diff --git a/pkgs/development/libraries/gmp/6.x.nix b/pkgs/development/libraries/gmp/6.x.nix
index 2635aed3eac..cb2c3f15da8 100644
--- a/pkgs/development/libraries/gmp/6.x.nix
+++ b/pkgs/development/libraries/gmp/6.x.nix
@@ -27,12 +27,13 @@ let self = stdenv.mkDerivation rec {
     # See <http://hydra.nixos.org/build/2760931>, for instance.
     #
     # no darwin because gmp uses ASM that clang doesn't like
-    optional (!stdenv.isSunOS) "--enable-fat"
+    optional (!stdenv.isSunOS && stdenv.hostPlatform.isx86) "--enable-fat"
     ++ (if cxx then [ "--enable-cxx"  ]
                else [ "--disable-cxx" ])
     ++ optional (cxx && stdenv.isDarwin) "CPPFLAGS=-fexceptions"
-    ++ optional stdenv.isDarwin "ABI=64"
+    ++ optional (stdenv.isDarwin && stdenv.is64bit) "ABI=64"
     ++ optional stdenv.is64bit "--with-pic"
+    ++ optional (with stdenv.hostPlatform; useAndroidPrebuilt || useiOSPrebuilt) "--disable-assembly"
     ;
 
   # The config.guess in GMP tries to runtime-detect various
@@ -75,7 +76,6 @@ let self = stdenv.mkDerivation rec {
          asymptotically faster algorithms.
       '';
 
-    broken = with stdenv.hostPlatform; useAndroidPrebuilt || useiOSPrebuilt;
     platforms = platforms.all;
     maintainers = [ maintainers.peti maintainers.vrthra ];
   };