diff --git a/apps/nc/CMakeLists.txt b/apps/nc/CMakeLists.txt
index f21c869..a241637 100644
--- a/apps/nc/CMakeLists.txt
+++ b/apps/nc/CMakeLists.txt
@@ -30,7 +30,8 @@ else()
 endif()
 
 check_function_exists(strtonum HAVE_STRTONUM)
-if(HAVE_STRTONUM)
+if(HAVE_STRTONUM AND CMAKE_SYSTEM_NAME MATCHES "Darwin" AND
+    CMAKE_HOST_SYSTEM_VERSION VERSION_GREATER_EQUAL 20)
 	add_definitions(-DHAVE_STRTONUM)
 else()
 	set(NC_SRC ${NC_SRC} compat/strtonum.c)
diff --git a/apps/ocspcheck/CMakeLists.txt b/apps/ocspcheck/CMakeLists.txt
index b960a81..43b091a 100644
--- a/apps/ocspcheck/CMakeLists.txt
+++ b/apps/ocspcheck/CMakeLists.txt
@@ -14,7 +14,8 @@ else()
 endif()
 
 check_function_exists(strtonum HAVE_STRTONUM)
-if(HAVE_STRTONUM)
+if(HAVE_STRTONUM AND CMAKE_SYSTEM_NAME MATCHES "Darwin" AND
+    CMAKE_HOST_SYSTEM_VERSION VERSION_GREATER_EQUAL 20)
 	add_definitions(-DHAVE_STRTONUM)
 else()
 	set(OCSPCHECK_SRC ${OCSPCHECK_SRC} compat/strtonum.c)
diff --git a/apps/openssl/CMakeLists.txt b/apps/openssl/CMakeLists.txt
index b9cd222..c5cfbe2 100644
--- a/apps/openssl/CMakeLists.txt
+++ b/apps/openssl/CMakeLists.txt
@@ -62,7 +62,8 @@ if(WIN32)
 endif()
 
 check_function_exists(strtonum HAVE_STRTONUM)
-if(HAVE_STRTONUM)
+if(HAVE_STRTONUM AND CMAKE_SYSTEM_NAME MATCHES "Darwin" AND
+    CMAKE_HOST_SYSTEM_VERSION VERSION_GREATER_EQUAL 20)
 	add_definitions(-DHAVE_STRTONUM)
 else()
 	set(OPENSSL_SRC ${OPENSSL_SRC} compat/strtonum.c)