diff --git a/pkgs/applications/science/logic/klee/default.nix b/pkgs/applications/science/logic/klee/default.nix
index 612d9fd57c7c..ae4b7ee36636 100644
--- a/pkgs/applications/science/logic/klee/default.nix
+++ b/pkgs/applications/science/logic/klee/default.nix
@@ -1,10 +1,9 @@
 { lib
 , callPackage
 , fetchFromGitHub
-, fetchpatch
 , cmake
-, llvmPackages_9
-, clang_9
+, llvmPackages_11
+, clang
 , python3
 , zlib
 , z3
@@ -36,31 +35,43 @@
 }:
 
 let
+
   # Python used for KLEE tests.
   kleePython = python3.withPackages (ps: with ps; [ tabulate ]);
 
   # The klee-uclibc derivation.
   kleeuClibc = callPackage ./klee-uclibc.nix {
-    inherit clang_9 llvmPackages_9 extraKleeuClibcConfig debugRuntime runtimeAsserts;
+    inherit clang llvmPackages_11 extraKleeuClibcConfig debugRuntime runtimeAsserts;
   };
+
 in
-clang_9.stdenv.mkDerivation rec {
+clang.stdenv.mkDerivation rec {
+
   pname = "klee";
-  version = "2.2";
+  version = "2.3";
+
   src = fetchFromGitHub {
     owner = "klee";
     repo = "klee";
     rev = "v${version}";
-    sha256 = "Ar3BKfADjJvvP0dI9+x/l3RDs8ncx4jmO7ol4MgOr4M=";
+    sha256 = "sha256-E1c6K6Q+LAWm342W8I00JI6+LMvqmULHZLkv9Kj5RmY=";
   };
+
   buildInputs = [
-    llvmPackages_9.llvm
-    z3 stp cryptominisat
-    gperftools sqlite
+    cryptominisat
+    gperftools
+    lit # Configure phase checking for lit
+    llvmPackages_11.llvm
+    sqlite
+    stp
+    z3
   ];
+
   nativeBuildInputs = [
-    cmake clang_9
+    clang
+    cmake
   ];
+
   checkInputs = [
     gtest
 
@@ -94,34 +105,7 @@ clang_9.stdenv.mkDerivation rec {
     patchShebangs .
   '';
 
-  patches = map fetchpatch [
-    /* This patch is currently necessary for the unit test suite to run correctly.
-     * See https://www.mail-archive.com/klee-dev@imperial.ac.uk/msg03136.html
-     * and https://github.com/klee/klee/pull/1458 for more information.
-     */
-    {
-      name = "fix-gtest";
-      sha256 = "F+/6videwJZz4sDF9lnV4B8lMx6W11KFJ0Q8t1qUDf4=";
-      url = "https://github.com/klee/klee/pull/1458.patch";
-    }
-
-    # This patch fixes test compile issues with glibc 2.33+.
-    {
-      name = "fix-glibc-2.33";
-      sha256 = "PzxqtFyLy9KF1eA9AAKg1tu+ggRdvu7leuvXifayIcc=";
-      url = "https://github.com/klee/klee/pull/1385.patch";
-    }
-
-    # /etc/mtab doesn't exist in the Nix build sandbox.
-    {
-      name = "fix-etc-mtab-in-tests";
-      sha256 = "2Yb/rJA791esNNqq8uAXV+MML4YXIjPKkHBOufvyRoQ=";
-      url = "https://github.com/klee/klee/pull/1471.patch";
-    }
-  ];
-
   doCheck = true;
-  checkTarget = "check";
 
   passthru = {
     # Let the user depend on `klee.uclibc` for klee-uclibc
diff --git a/pkgs/applications/science/logic/klee/klee-uclibc.nix b/pkgs/applications/science/logic/klee/klee-uclibc.nix
index 2e3826c50c42..a794fe2eee8a 100644
--- a/pkgs/applications/science/logic/klee/klee-uclibc.nix
+++ b/pkgs/applications/science/logic/klee/klee-uclibc.nix
@@ -3,9 +3,10 @@
 , fetchFromGitHub
 , which
 , linuxHeaders
-, clang_9
-, llvmPackages_9
+, clang
+, llvmPackages_11
 , python3
+, curl
 , debugRuntime ? true
 , runtimeAsserts ? false
 , extraKleeuClibcConfig ? {}
@@ -23,18 +24,20 @@ let
     "DEVEL_PREFIX" = "/";
   });
 in
-clang_9.stdenv.mkDerivation rec {
+clang.stdenv.mkDerivation rec {
   pname = "klee-uclibc";
-  version = "1.2";
+  version = "1.3";
   src = fetchFromGitHub {
     owner = "klee";
     repo = "klee-uclibc";
     rev = "klee_uclibc_v${version}";
-    sha256 = "qdrGMw+2XwpDsfxdv6swnoaoACcF5a/RWgUxUYbtPrI=";
+    sha256 = "sha256-xQ8GWa0Gmd3lbwKodJhrsZeuR4j7NT4zIUh+kNhVY/w=";
   };
+
   nativeBuildInputs = [
-    clang_9
-    llvmPackages_9.llvm
+    clang
+    curl
+    llvmPackages_11.llvm
     python3
     which
   ];
@@ -44,7 +47,7 @@ clang_9.stdenv.mkDerivation rec {
 
   # HACK: needed for cross-compile.
   # See https://www.mail-archive.com/klee-dev@imperial.ac.uk/msg03141.html
-  KLEE_CFLAGS = "-idirafter ${clang_9}/resource-root/include";
+  KLEE_CFLAGS = "-idirafter ${clang}/resource-root/include";
 
   prePatch = ''
     patchShebangs ./configure