diff --git a/rtl/bsd/sysctl.pp b/rtl/bsd/sysctl.pp
index dce63aac8a..38e39e5d44 100644
--- a/rtl/bsd/sysctl.pp
+++ b/rtl/bsd/sysctl.pp
@@ -84,9 +84,9 @@ TYPE    CtlNameRec = Record
 //
 
 {$ifdef FPC_USE_LIBC}
-function FPsysctl (Name: pchar; namelen:cuint; oldp:pointer;oldlenp:psize_t; newp:pointer;newlen:size_t):cint; external name 'sysctl';
-function FPsysctlbyname (Name: pchar; oldp:pointer;oldlenp:psize_t; newp:pointer;newlen:size_t):cint; external name 'sysctlbyname';
-function FPsysctlnametomib (Name: pchar;mibp:plongint;sizep:psize_t):cint; external name 'sysctltomib';
+function FPsysctl (Name: pchar; namelen:cuint; oldp:pointer;oldlenp:psize_t; newp:pointer;newlen:size_t):cint; cdecl; external name 'sysctl';
+function FPsysctlbyname (Name: pchar; oldp:pointer;oldlenp:psize_t; newp:pointer;newlen:size_t):cint; cdecl; external name 'sysctlbyname';
+function FPsysctlnametomib (Name: pchar;mibp:plongint;sizep:psize_t):cint; cdecl; external name 'sysctltomib';
 {$else}
 function FPsysctl (Name: pchar; namelen:cuint; oldp:pointer;oldlenp:psize_t; newp:pointer;newlen:size_t):cint;
 function FPsysctlbyname (Name: pchar; oldp:pointer;oldlenp:psize_t; newp:pointer;newlen:size_t):cint;