diff --git a/pkgs/development/libraries/libiscsi/default.nix b/pkgs/development/libraries/libiscsi/default.nix
index 826593b9d66c..1008037c60cc 100644
--- a/pkgs/development/libraries/libiscsi/default.nix
+++ b/pkgs/development/libraries/libiscsi/default.nix
@@ -2,24 +2,26 @@
 
 stdenv.mkDerivation rec {
   pname = "libiscsi";
-  version = "1.19.0";
+  version = "1.20.0";
 
   src = fetchFromGitHub {
     owner = "sahlberg";
     repo = "libiscsi";
     rev = version;
-    sha256 = "0ajrkkg5awmi8m4b3mha7h07ylg18k252qprvk1sgq0qbyd66zy7";
+    sha256 = "sha256-idiK9JowKhGAk5F5qJ57X14Q2Y0TbIKRI02onzLPkas=";
   };
 
   postPatch = ''
     substituteInPlace lib/socket.c \
-      --replace "void iscsi_decrement_iface_rr() {" "void iscsi_decrement_iface_rr(void) {"
+      --replace-fail "void iscsi_decrement_iface_rr() {" "void iscsi_decrement_iface_rr(void) {"
   '';
 
   nativeBuildInputs = [ autoreconfHook ];
 
-  # This problem is gone on libiscsi master.
-  env.NIX_CFLAGS_COMPILE = toString (lib.optional stdenv.hostPlatform.is32bit "-Wno-error=sign-compare");
+  env = lib.optionalAttrs (stdenv.is32bit || stdenv.isDarwin) {
+    # iscsi-discard.c:223:57: error: format specifies type 'unsigned long' but the argument has type 'uint64_t' (aka 'unsigned long long') [-Werror,-Wformat]
+    NIX_CFLAGS_COMPILE = "-Wno-error=format";
+  };
 
   meta = with lib; {
     description = "iscsi client library and utilities";