diff --git a/pkgs/by-name/tr/transgui/package.nix b/pkgs/by-name/tr/transgui/package.nix
index 23286a131448..fb78b119b537 100644
--- a/pkgs/by-name/tr/transgui/package.nix
+++ b/pkgs/by-name/tr/transgui/package.nix
@@ -55,6 +55,9 @@ stdenv.mkDerivation rec {
 
   postPatch = ''
     substituteInPlace restranslator.pas --replace /usr/ $out/
+
+    # Fix build with lazarus 4.0, https://github.com/transmission-remote-gui/transgui/issues/1486
+    substituteInPlace main.pas --replace-warn "h <> INVALID_HANDLE_VALUE" "h >= 0"
   '';
 
   preBuild = ''
diff --git a/pkgs/development/compilers/fpc/lazarus.nix b/pkgs/development/compilers/fpc/lazarus.nix
index 56f36a2b59bf..236748501791 100644
--- a/pkgs/development/compilers/fpc/lazarus.nix
+++ b/pkgs/development/compilers/fpc/lazarus.nix
@@ -27,7 +27,7 @@
 #  1. the build date is embedded in the binary through `$I %DATE%` - we should dump that
 
 let
-  version = "3.6-0";
+  version = "4.0-0";
 
   # as of 2.0.10 a suffix is being added. That may or may not disappear and then
   # come back, so just leave this here.
@@ -51,7 +51,7 @@ stdenv.mkDerivation rec {
 
   src = fetchurl {
     url = "mirror://sourceforge/lazarus/Lazarus%20Zip%20_%20GZip/Lazarus%20${majorMinorPatch version}/lazarus-${version}.tar.gz";
-    hash = "sha256-5luQNn9jvxfLe/NfW+acnvcEyklOkdjGfQcuM3P6sIU=";
+    hash = "sha256-vIM7RxzXqCYSiavND1OhFjuMcG5FmD+zq6kmEiM5z8s=";
   };
 
   postPatch = ''