diff --git a/pkgs/top-level/dotnet-packages.nix b/pkgs/top-level/dotnet-packages.nix
index 1a37d58c70d1..43182b3f2aaa 100644
--- a/pkgs/top-level/dotnet-packages.nix
+++ b/pkgs/top-level/dotnet-packages.nix
@@ -331,13 +331,20 @@ let self = dotnetPackages // overrides; dotnetPackages = with self; {
 
   Dafny = buildDotnetPackage rec {
     baseName = "Dafny";
-    version = "1.9.8";
+    version = "2.1.0";
 
     src = fetchurl {
       url = "https://github.com/Microsoft/dafny/archive/v${version}.tar.gz";
-      sha256 = "0n4pk4cv7d2zsn4xmyjlxvpfl9avq79r06c7kzmrng24p3k4qj6s";
+      sha256 = "1iyhy0zpi6wvqif7826anzgdipgsy5bk775ds9qqwfw27j7x6fy5";
     };
 
+    postPatch = ''
+      sed -i \
+        -e 's/ Visible="False"//' \
+        -e "s/Exists(\$(CodeContractsInstallDir))/Exists('\$(CodeContractsInstallDir)')/" \
+        Source/*/*.csproj
+    '';
+
     preBuild = ''
       ln -s ${pkgs.z3} Binaries/z3
     '';
@@ -345,7 +352,7 @@ let self = dotnetPackages // overrides; dotnetPackages = with self; {
     buildInputs = [ Boogie ];
 
     xBuildFiles = [ "Source/Dafny.sln" ];
-    xBuildFlags = [ ];
+    xBuildFlags = [ "/p:Configuration=Checked" "/p:Platform=Any CPU" "/t:Rebuild" ];
 
     outputFiles = [ "Binaries/*" ];