diff --git a/winsup/cygwin/cygmagic b/winsup/cygwin/cygmagic
index b94529109..036c79c11 100755
--- a/winsup/cygwin/cygmagic
+++ b/winsup/cygwin/cygmagic
@@ -24,7 +24,7 @@ sumit() {
 while [ -n "$1" ]; do
     define=$1; shift
     struct=$1; shift
-    sum=`$gcc -D__CYGMAGIC__ -E $file | sed -n "/^$struct/,/^};/p" | sed -e 's/[ 	]//g' -e '/^$/d' | sumit | awk '{printf "0x%xU", $1}'`
+    sum=`$gcc -D__CYGMAGIC__ -E -P $file | sed -n "/^$struct/,/^};/p" | sed -e 's/[ 	]//g' -e '/^$/d' | sumit | awk '{printf "0x%xU", $1}'`
     echo "#define $define $sum"
     curr=`sed -n "s/^#[ 	]*define CURR_$define[ 	][ 	]*\([^ 	][^ 	]*\)/\1/p" $file`
     [ "$curr" != "$sum" ] && echo "*** WARNING WARNING WARNING WARNING WARNING ***