diff --git a/cmake/modules/HandleLLVMOptions.cmake b/cmake/modules/HandleLLVMOptions.cmake
index 2ee0dd5b1b7..e60018e6a0d 100644
--- a/cmake/modules/HandleLLVMOptions.cmake
+++ b/cmake/modules/HandleLLVMOptions.cmake
@@ -104,6 +104,13 @@ if(APPLE)
   set(CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS} -Wl,-flat_namespace -Wl,-undefined -Wl,suppress")
 endif()
 
+# Pass -Wl,-z,defs. This makes sure all symbols are defined. Otherwise a DSO
+# build might work on ELF but fail on MachO/COFF.
+if(NOT (${CMAKE_SYSTEM_NAME} MATCHES "Darwin" OR WIN32))
+  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,-z,defs")
+endif()
+
+
 function(append value)
   foreach(variable ${ARGN})
     set(${variable} "${${variable}} ${value}" PARENT_SCOPE)
diff --git a/utils/unittest/CMakeLists.txt b/utils/unittest/CMakeLists.txt
index b6d2d6d9e0e..7ac894dff14 100644
--- a/utils/unittest/CMakeLists.txt
+++ b/utils/unittest/CMakeLists.txt
@@ -38,11 +38,20 @@ if(MSVC AND MSVC_VERSION EQUAL 1700)
   add_definitions(-D_VARIADIC_MAX=10)
 endif ()
 
+set(LIBS
+  LLVMSupport # Depends on llvm::raw_ostream
+)
+
+find_library(PTHREAD_LIBRARY_PATH pthread)
+if (PTHREAD_LIBRARY_PATH)
+  list(APPEND LIBS pthread)
+endif()
+
 add_llvm_library(gtest
   googletest/src/gtest-all.cc
 
   LINK_LIBS
-  LLVMSupport # Depends on llvm::raw_ostream
-  )
+  ${LIBS}
+)
 
 add_subdirectory(UnitTestMain)