diff --git a/pkgs/development/compilers/mono/4.nix b/pkgs/development/compilers/mono/4.nix
index 0bbf90767d48..66d8ff8a010a 100644
--- a/pkgs/development/compilers/mono/4.nix
+++ b/pkgs/development/compilers/mono/4.nix
@@ -12,4 +12,11 @@ callPackage ./generic.nix ({
   sha256 = "1vyvp2g28ihcgxgxr8nhzyzdmzicsh5djzk8dk1hj5p5f2k3ijqq";
   enableParallelBuilding = false; # #32386, https://hydra.nixos.org/build/65600645
   extraPatches = lib.optionals stdenv.hostPlatform.isLinux [ ./mono4-glibc.patch ];
+  env.NIX_CFLAGS_COMPILE = toString [
+    "-Wno-error=implicit-function-declaration"
+    "-Wno-error=implicit-int"
+    "-Wno-error=incompatible-pointer-types"
+    "-Wno-error=int-conversion"
+    "-Wno-error=return-mismatch"
+  ];
 })
diff --git a/pkgs/development/compilers/mono/5.nix b/pkgs/development/compilers/mono/5.nix
index 18daf8e641a5..4cf7252dcc35 100644
--- a/pkgs/development/compilers/mono/5.nix
+++ b/pkgs/development/compilers/mono/5.nix
@@ -9,4 +9,5 @@ callPackage ./generic.nix ({
   version = "5.20.1.34";
   sha256 = "12vw5dkhmp1vk9l658pil8jiqirkpdsc5z8dm5mpj595yr6d94fd";
   enableParallelBuilding = true;
+  env.NIX_CFLAGS_COMPILE = "-Wno-error=incompatible-pointer-types -Wno-error=implicit-function-declaration";
 })
diff --git a/pkgs/development/compilers/mono/generic.nix b/pkgs/development/compilers/mono/generic.nix
index d9e34223771c..ffa2d78bab18 100644
--- a/pkgs/development/compilers/mono/generic.nix
+++ b/pkgs/development/compilers/mono/generic.nix
@@ -29,6 +29,7 @@
   enableParallelBuilding ? true,
   srcArchiveSuffix ? "tar.bz2",
   extraPatches ? [ ],
+  env ? { },
 }:
 
 let
@@ -36,7 +37,7 @@ let
 in
 stdenv.mkDerivation rec {
   pname = "mono";
-  inherit version;
+  inherit version env;
 
   src = fetchurl {
     inherit sha256;
diff --git a/pkgs/development/libraries/gtk-sharp/2.0.nix b/pkgs/development/libraries/gtk-sharp/2.0.nix
index 120b39ced22a..8981e4df3981 100644
--- a/pkgs/development/libraries/gtk-sharp/2.0.nix
+++ b/pkgs/development/libraries/gtk-sharp/2.0.nix
@@ -64,11 +64,7 @@ stdenv.mkDerivation rec {
     ./bootstrap-${lib.versions.majorMinor version}
   '';
 
-  env.NIX_CFLAGS_COMPILE = toString (
-    lib.optionals stdenv.cc.isClang [
-      "-Wno-error=int-conversion"
-    ]
-  );
+  env.NIX_CFLAGS_COMPILE = "-Wno-error=int-conversion";
 
   dontStrip = true;
 
diff --git a/pkgs/development/libraries/gtk-sharp/3.0.nix b/pkgs/development/libraries/gtk-sharp/3.0.nix
index 98ccf2a111de..89121db3b5d4 100644
--- a/pkgs/development/libraries/gtk-sharp/3.0.nix
+++ b/pkgs/development/libraries/gtk-sharp/3.0.nix
@@ -31,6 +31,8 @@ stdenv.mkDerivation rec {
     libxml2
   ];
 
+  env.NIX_CFLAGS_COMPILE = "-Wno-error=implicit-function-declaration";
+
   patches = [
     # Fixes MONO_PROFILE_ENTER_LEAVE undeclared when compiling against newer versions of mono.
     # @see https://github.com/mono/gtk-sharp/pull/266