Index: yubico-piv-tool-2.2.1/ykcs11/CMakeLists.txt
===================================================================
--- yubico-piv-tool-2.2.1.orig/ykcs11/CMakeLists.txt
+++ yubico-piv-tool-2.2.1/ykcs11/CMakeLists.txt
@@ -60,6 +60,9 @@ if(${ENABLE_HARDWARE_TESTS})
     set(HW_TESTS 1)
 endif(${ENABLE_HARDWARE_TESTS})
 
+set(THREADS_PREFER_PTHREAD_FLAG ON)
+find_package(Threads REQUIRED)
+
 # static library
 if(BUILD_STATIC_LIB)
     add_library(ykcs11 STATIC ${SOURCE})
@@ -73,7 +76,7 @@ endif(BUILD_STATIC_LIB)
 
 # dynamic library
 add_library(ykcs11_shared SHARED ${SOURCE})
-target_link_libraries(ykcs11_shared ${LIBCRYPTO_LDFLAGS} ykpiv_shared)
+target_link_libraries(ykcs11_shared ${LIBCRYPTO_LDFLAGS} ykpiv_shared Threads::Threads)
 set_target_properties(ykcs11_shared PROPERTIES SOVERSION ${SO_VERSION} VERSION ${VERSION})
 if (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
     set_target_properties(ykcs11_shared PROPERTIES INSTALL_RPATH "${YKPIV_INSTALL_LIB_DIR}")