--- a/src/auto/configure
+++ b/src/auto/configure
@@ -4426,15 +4426,18 @@ case `uname` in
 		  echo ""
 		  echo "------------------------------------------"
 		  echo " On z/OS Unix, the environment variable"
-		  echo " __CC_${ccn}MODE must be set to \"1\"!"
+		  echo " _CC_${ccn}MODE must be set to \"1\"!"
 		  echo " Do:"
 		  echo "    export _CC_${ccn}MODE=1"
 		  echo " and then call configure again."
 		  echo "------------------------------------------"
 		  exit 1
 		fi
-		CFLAGS="$CFLAGS -D_ALL_SOURCE -Wc,float\\(IEEE\\)";
-                LDFLAGS="$LDFLAGS -Wl,EDIT=NO"
+		# Set CFLAGS for configure process.
+		# This will be reset later for config.mk.
+		# Use haltonmsg to force error for missing H files.
+		CFLAGS="$CFLAGS -D_ALL_SOURCE -Wc,float(ieee),haltonmsg(3296)";
+		LDFLAGS="$LDFLAGS -Wl,EDIT=NO"
 		{ $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 $as_echo "yes" >&6; }
 		;;
@@ -8697,8 +8700,13 @@ fi
 if test -z "$SKIP_MOTIF"; then
   cppflags_save=$CPPFLAGS
   CPPFLAGS="$CPPFLAGS $X_CFLAGS"
-  for ac_header in Xm/Xm.h Xm/XpmP.h Xm/JoinSideT.h Xm/TraitP.h Xm/Manager.h \
-		   Xm/UnhighlightT.h Xm/Notebook.h
+  if test "$zOSUnix" = "yes"; then
+	xmheader="Xm/Xm.h"
+  else
+	xmheader="Xm/Xm.h Xm/XpmP.h Xm/JoinSideT.h Xm/TraitP.h Xm/Manager.h
+  	   Xm/UnhighlightT.h Xm/Notebook.h"
+  fi
+  for ac_header in $xmheader
 do :
   as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
 ac_fn_c_check_header_mongrel "$LINENO" "$ac_header" "$as_ac_Header" "$ac_includes_default"
@@ -8713,7 +8721,7 @@ fi
 done
 
 
-  if test $ac_cv_header_Xm_XpmP_h = yes; then
+  if test "x$ac_cv_header_Xm_XpmP_h" = "xyes"; then
         { $as_echo "$as_me:${as_lineno-$LINENO}: checking for XpmAttributes_21 in Xm/XpmP.h" >&5
 $as_echo_n "checking for XpmAttributes_21 in Xm/XpmP.h... " >&6; }
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
@@ -12590,6 +12598,11 @@ else
 fi
 
 
+# IBM z/OS reset CFLAGS for config.mk
+if test "$zOSUnix" = "yes"; then
+	CFLAGS="-D_ALL_SOURCE -Wc,float\(ieee\),dll"
+fi
+
 ac_config_files="$ac_config_files auto/config.mk:config.mk.in"
 
 cat >confcache <<\_ACEOF