diff --git a/.cmake/libstd-memcheck.mk b/.cmake/libstd-memcheck.mk
new file mode 100644
index 00000000..62e1048c
--- /dev/null
+++ b/.cmake/libstd-memcheck.mk
@@ -0,0 +1,14 @@
+include(ExternalProject)
+string (REPLACE " " "$<SEMICOLON>" LLVM_PROJECT_TARGETS "libcxx libcxxabi")
+set(PREFIX ${CMAKE_CURRENT_BINARY_DIR}/3rd/llvm-project)
+ExternalProject_Add(
+  llvm-project
+  GIT_REPOSITORY    https://github.com/llvm/llvm-project.git
+  GIT_TAG           llvmorg-12.0.0
+  GIT_SHALLOW       TRUE
+  CMAKE_ARGS        -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS=${LLVM_PROJECT_TARGETS} -DLLVM_USE_SANITIZER=MemoryWithOrigins -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ ../llvm-project/llvm
+  BUILD_COMMAND     make cxx cxxabi
+  INSTALL_COMMAND   DESTDIR=${PREFIX} make install-cxx-headers install-cxx install-cxxabi
+  COMMENT           "Building memcheck instrumented libc++ and libc++abi"
+  PREFIX            ${PREFIX}
+)
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index d2c3ca56..2df860ff 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -21,7 +21,8 @@ jobs:
           clang-release-build,
           gcc-debug-build,
           clang-debug-build,
-          clang-debug-asan-build,
+          clang-release-asan-build,
+          clang-release-msan-build,
         ]
 
         include:
@@ -41,10 +42,14 @@ jobs:
             cc: /usr/bin/clang
             cxx: /usr/bin/clang++
             flags: -DCMAKE_BUILD_TYPE=Debug
-          - name: clang-debug-asan-build
+          - name: clang-release-asan-build
             cc: clang
             cxx: clang++
             flags: -DCMAKE_BUILD_TYPE=Release -DADDRSAN=1
+          - name: clang-release-msan-build
+            cc: clang
+            cxx: clang++
+            flags: -DCMAKE_BUILD_TYPE=Release -DMEMSAN=1
     steps:
       - uses: actions/checkout@v1
         with:
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 70429e67..796f4e6d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -24,6 +24,7 @@ FetchContent_Declare(
   SOURCE_DIR     ${PROJECT_SOURCE_DIR}/3rd/cpu_features
   GIT_REPOSITORY https://github.com/google/cpu_features.git
   GIT_TAG        bc2846e78faeb26b8a46c17df369d4e5f1f9e2bb
+  GIT_SHALLOW    TRUE
 )
 FetchContent_Populate(cpu_features)
 
@@ -32,9 +33,22 @@ FetchContent_Declare(
   SOURCE_DIR     ${PROJECT_SOURCE_DIR}/3rd/gbench
   GIT_REPOSITORY https://github.com/kriskwiatkowski/benchmark.git
   GIT_TAG        49862ab56b6b7c3afd87b80bd5d787ed78ce3b96
+  GIT_SHALLOW    TRUE
 )
 FetchContent_Populate(gbench)
 
+if(MEMSAN)
+  # PQC_MEMSAN enables usage of some internals from clang
+  if (NOT CMAKE_C_COMPILER_ID MATCHES "Clang")
+    message(FATAL_ERROR "Must use clang if compiled with memory sanitizer.")
+  endif()
+  if(ADDRSAN)
+    message(FATAL_ERROR "Can't use MSAN and ASAN")
+  endif()
+  include(.cmake/libstd-memcheck.mk)
+  #set(C_CXX_FLAGS "${C_CXX_FLAGS} -DPQC_MEMSAN=1 -fsanitize=memory -fsanitize-memory-track-origins=2 -fno-omit-frame-pointer")
+endif()
+
 add_subdirectory(3rd/gtest)
 set(BUILD_PIC ON CACHE BOOL "")
 add_subdirectory(3rd/cpu_features)
@@ -117,19 +131,6 @@ if(ADDRSAN)
   set(LDFLAGS "${LDFLAGS} -fsanitize=undefined,address,leak")
 endif()
 
-# Build with memory sanitizer
-if(MEMSAN)
-  # PQC_MEMSAN enables usage of some internals from clang
-  if (NOT CMAKE_C_COMPILER_ID MATCHES "Clang")
-    message(FATAL_ERROR "Must use clang if compiled with memory sanitizer.")
-  endif()
-  if(ADDRSAN)
-    message(FATAL_ERROR "Can't use MSAN and ASAN")
-  endif()
-
-  set(C_CXX_FLAGS "${C_CXX_FLAGS} -DPQC_MEMSAN=1 -fsanitize=memory -fsanitize-memory-track-origins=2 -fno-omit-frame-pointer")
-endif()
-
 include(.cmake/common.mk)
 
 # Control Debug/Release mode
diff --git a/test/ct.cpp b/test/ct.cpp
new file mode 100644
index 00000000..73d79f20
--- /dev/null
+++ b/test/ct.cpp
@@ -0,0 +1,23 @@
+#include <algorithm>
+#include <vector>
+#include <gtest/gtest.h>
+#include <pqc/pqc.h>
+
+// #ifdef VALGRIND
+// #include <valgrind/valgrind.h>
+// #include <valgrind/memcheck.h>
+// #define POISON(p,sz) VALGRIND_MAKE_MEM_UNDEFINED(p,sz)
+// #endif
+
+#ifdef PQC_MEMSAN
+#include <sanitizer/msan_interface.h>
+#define POISON(p,sz) __msan_poison(p,sz)
+#endif
+
+
+TEST(ConstantTime, Poisonner_Basic) {
+	unsigned char x[8] = {0};
+//gi	POISON(x, 4);
+	if(x[5]) x[6] = x[5];
+	//UNPOISON(x, 4);
+}