diff --git a/rtl/unix/scripts/check_sys.sh b/rtl/unix/scripts/check_sys.sh
index c3c265d912..fc317cfd43 100755
--- a/rtl/unix/scripts/check_sys.sh
+++ b/rtl/unix/scripts/check_sys.sh
@@ -4,18 +4,63 @@
 
 # Location of syscall header in system
 
-syscall_header=/usr/include/sys/syscall.h
+syscall_header=/usr/include/syscall.h
+fpc_sysnr=./sysnr.inc
+
+if ! [ -f $fpc_sysnr ] ; then
+  cpu=`fpc -iTP`
+  fpc_sysnr=./$cpu/sysnr.inc
+fi
 
 verbose=0
 
+os=`uname -s`
+
+# Test C file to grab all loaded headers
+cat > test-syscall.c <<EOF
+#include <syscall.h>
+
+int
+main ()
+{
+  return 0;
+}
+EOF
+
+# Default C compiler is gcc
+# Can be overwritten by setting CC variable
+# But I don't know if other compilers also generate
+# .i files with --save-temps option
+if [ "$CC" == "" ] ; then
+  CC=gcc
+fi
+
+# Use gcc with --save-temps option to create .i file
+$CC --save-temps -o test-syscall ./test-syscall.c
+# list of errno.h headers listed
+syscall_headers=` sed -n "s:.*\"\(.*/.*\.h\)\".*:\1:p" test-syscall.i |sort | uniq`
+echo "Headers found are \"$syscall_headers\""
+
+if [ "$syscall_headers" != "" ] ; then
+  syscall_header="$syscall_headers"
+fi
+
+
 # Sustitution made to pass from fpc syscall number
 # to system define 
 fpc_syscall_prefix=syscall_nr_
-syscall_prefix=SYS_
+if [ "$os" == "Linux" ] ; then
+  # On Linux system, system call number are defined indirectly
+  # with #define SYS_XXX __NR_XXX
+  # We look directly for the __NT_ version
+  syscall_prefix=__NR_
+else
+  syscall_prefix=SYS_
+fi
 
 # You should only need to change the variables above
 
-sed -n "s:^[ \t]*${fpc_syscall_prefix}\\([_a-zA-Z0-9]*\\)[ \t]*=[ \t]*\\([0-9]*\\).*:check_syscall_number ${syscall_prefix}\1 \2:p" sysnr.inc > check_sys_list.sh
+sed -n "s:^[ \t]*${fpc_syscall_prefix}\\([_a-zA-Z0-9]*\\)[ \t]*=[ \t]*\\([0-9]*\\).*:check_syscall_number ${syscall_prefix}\1 \2:p" ${fpc_sysnr} > check_sys_list.sh
 
 function check_syscall_number ()
 {
@@ -24,8 +69,8 @@ function check_syscall_number ()
   if [ $verbose -ne 0 ] ; then
     echo Testing $sys value $value
   fi
-  found=`sed -n "/#define.*${sys}[^A-Za-z0-9_]/p" ${syscall_header}`
-  val=`sed -n "s:#define.*${sys}[^A-Za-z0-9_][^A-Za-z0-9_]*\([0-9]*\).*:\1:p" ${syscall_header}`
+  found=`sed -n "/#define[[:space:]]*${sys}[^A-Za-z0-9_]/p" ${syscall_header}`
+  val=`sed -n "s:#define[[:space:]]*${sys}[^A-Za-z0-9_][^A-Za-z0-9_]*\([0-9]*\).*:\1:p" ${syscall_header}`
   if [ $verbose -ne 0 ] ; then
     echo Test for $sys found \"${found}\" \"${value}\" \"${val}\"
   fi
@@ -40,9 +85,13 @@ function check_syscall_number ()
         found=`sed -n "s:\/\* ${value} is compa: ${value} is compa:p" ${syscall_header}`
       fi
     fi
+    if [ "$found" == "" ] ; then
+      found=`grep -n -w $value ${syscall_header}`
+    fi
     echo problem for ${sys} expected ${value}, line is \"${found}\", val found is \"${val}\"
   fi
 }
 
+echo "Checking in ${syscall_header}"
 source ./check_sys_list.sh