diff --git a/rtl/inc/os_types.pp b/rtl/inc/os_types.pp
new file mode 100644
index 0000000000..d66d928ade
--- /dev/null
+++ b/rtl/inc/os_types.pp
@@ -0,0 +1,66 @@
+UNIT os_types;
+
+{ 
+  Note: 
+  This file is meant as a helper for porting C and C++ interfaces to FreePascal. 
+  It got required since FPC's resolving of the integer type depends on selected
+  slang but not much on the target platform like its state of the art in C. 
+  When porting API interfaces its recomended to use the types defined here.
+  2000-Mar-18   alex    <AlexS@freepage.de>
+}
+
+INTERFACE
+
+TYPE
+// ordinal types
+{$ifdef Go32v1}
+  tOS_INT  = LongInt;
+  tOS_UINT = DWord;
+{$define OS_TYPES}
+{$endif}
+{$ifdef Go32v2}
+  tOS_INT  = LongInt;
+  tOS_UINT = DWord;
+{$define OS_TYPES}
+{$endif}
+{$ifdef WIN16}
+  tOS_INT  = SmallInt;
+  tOS_UINT = Word;
+{$define OS_TYPES}
+{$endif}
+{$ifdef WIN32}
+  tOS_INT  = LongInt;
+  tOS_UINT = DWord;
+{$define OS_TYPES}
+{$endif}
+{$ifdef WIN64}
+  tOS_INT  = Comp;  { 8 byte signed ordinal }
+  tOS_UINT = QWord; { 8 byte unsigned ordinal }{ possibly still needs to be defined }
+{$define OS_TYPES}
+{$endif}
+{$ifdef LINUX}
+{ TODO - how can we decide if we run on a 32 or a 64 bit linux platform ??? }
+  tOS_INT  = LongInt;
+  tOS_UINT = DWord;
+{$define OS_TYPES}
+{$endif}
+{$ifdef OS2}
+{ TODO - just an assumption }
+  tOS_INT  = LongInt;
+  tOS_UINT = DWord;
+{$define OS_TYPES}
+{$endif}
+
+{$ifdef OS_TYPES}
+// derive pointers from base types
+  ptOS_INT = ^tOS_INT;
+  ptOS_UINT = ^tOS_UINT;
+{$else}
+{$warning In Unit OS_Types: no case for your target present }
+{$endif}
+
+IMPLEMENTATION
+
+{begin}{of init}
+end.
+