diff --git a/cmake/PlatformDefaults.cmake b/cmake/PlatformDefaults.cmake
index 01050c8df..a621124b8 100644
--- a/cmake/PlatformDefaults.cmake
+++ b/cmake/PlatformDefaults.cmake
@@ -1,23 +1,61 @@
-# default defines or other required preferences per platform
-if((CMAKE_SYSTEM_NAME MATCHES "WindowsStore") AND (CMAKE_SYSTEM_VERSION MATCHES "10.0"))
-    set(UWP 1 CACHE BOOL "platform default")
-	add_definitions("-D_UWP")
-    set(CMAKE_WINDOWS_VERSION "WIN10" CACHE STRING "platform default")
-endif()
+# This option allows deactivating FreeRDP supplied platform defauts to replace these with
+# user supplied values.
+#
+# Compilation will fail without a replacement defining the symbols, but that can be
+# done by supplying a TOOLCHAIN_FILE defining these.
+option(USE_PLATFORM_DEFAULT "Use this configuration file for platform defaults. Supply -DCMAKE_TOOLCHAIN_FILE=<yourfile> otherwise." ON)
+if (USE_PLATFORM_DEFAULT)
+    # default defines or other required preferences per platform
+    if((CMAKE_SYSTEM_NAME MATCHES "WindowsStore") AND (CMAKE_SYSTEM_VERSION MATCHES "10.0"))
+        set(UWP 1 CACHE BOOL "platform default")
+        add_definitions("-D_UWP")
+        set(CMAKE_WINDOWS_VERSION "WIN10" CACHE STRING "platform default")
+    endif()
 
-if("${CMAKE_SYSTEM_NAME}" MATCHES "Linux")
-	add_definitions("-D_FILE_OFFSET_BITS=64")
-    add_definitions("-DWINPR_TIMEZONE_FILE=\"/etc/timezone\"")
-endif()
+    if("${CMAKE_SYSTEM_NAME}" MATCHES "Linux")
+        # Linux already does define _POSIX_C_SOURCE by default, nothing to do
+        add_definitions("-D_FILE_OFFSET_BITS=64")
+        set(WINPR_TIMEZONE_FILE "/etc/timezone")
+    endif()
 
-if("${CMAKE_SYSTEM_NAME}" MATCHES "FreeBSD")
-	add_definitions("-D_FILE_OFFSET_BITS=64")
-    add_definitions("-DWINPR_TIMEZONE_FILE=\"/var/db/zoneinfo\"")
-endif()
+    if("${CMAKE_SYSTEM_NAME}" MATCHES "FreeBSD")
+        # we want POSIX 2008. FreeBSD 14 does only support 2001 fully, but the subset we require from 2008
+        # is implemented, so ignore _POSIX_VERSION from unistd.h
+        add_definitions("-D_POSIX_C_SOURCE=200809L")
+        # TODO: FreeBSD allows mixing POSIX and BSD API calls if we do not set
+        # _POSIX_C_SOURCE but lack a macro to reenable the BSD calls...
+        add_definitions("-D__BSD_VISIBLE")
 
-if("${CMAKE_SYSTEM_NAME}" MATCHES "SunOS")
-	add_definitions("-D_POSIX_PTHREAD_SEMANTICS")
-    list(APPEND CMAKE_STANDARD_LIBRARIES rt)
-    set(CMAKE_STANDARD_LIBRARIES ${CMAKE_STANDARD_LIBRARIES} CACHE STRING "platform default")
-    set(WITH_SUN true CACHE BOOL "platform default")
+        # There are some symbols only visible for XOpen standard
+        add_definitions("-D_XOPEN_SOURCE=700")
+        add_definitions("-D_FILE_OFFSET_BITS=64")
+        set(WINPR_TIMEZONE_FILE "/var/db/zoneinfo")
+    endif()
+
+    if("${CMAKE_SYSTEM_NAME}" MATCHES "SunOS")
+        # TODO: Does somebody still use this? please show yourself and
+        # tell us if this still works.
+        add_definitions("-D_POSIX_PTHREAD_SEMANTICS")
+        list(APPEND CMAKE_STANDARD_LIBRARIES rt)
+        set(CMAKE_STANDARD_LIBRARIES ${CMAKE_STANDARD_LIBRARIES} CACHE STRING "platform default")
+        set(WITH_SUN true CACHE BOOL "platform default")
+    endif()
+
+    if("${CMAKE_SYSTEM_NAME}" MATCHES "Darwin")
+        # we want POSIX 2008. MacOS does only support 2001 fully, but the subset we require from 2008
+        # is implemented, so ignore _POSIX_VERSION from unistd.h
+        add_definitions("-D_POSIX_C_SOURCE=200809L")
+
+        # as _POSIX_C_SOURCE sets a fully POSIX confirmant environment reenable
+        # MacOS API visibility by defining the following feature test macro
+        add_definitions("-D_DARWIN_C_SOURCE")
+    endif()
+
+    # define a fallback for systems that do not support a timezone file or we did not yet test.
+    # since most of these are BSD try a sensible default
+    if (NOT WINPR_TIMEZONE_FILE)
+        set(WINPR_TIMEZONE_FILE "/var/db/zoneinfo")
+    endif()
+
+    add_definitions("-DWINPR_TIMEZONE_FILE=\"${WINPR_TIMEZONE_FILE}\"")
 endif()