diff --git a/configure b/configure
index bc723443e..4de1e5ce2 100755
--- a/configure
+++ b/configure
@@ -650,7 +650,7 @@ cat > $test.c <<EOF
 int main() { return 0; }
 EOF
 if try $CC -c $CFLAGS $test.c; then
-  sed < zconf.h "/^#if HAVE_UNISTD_H-0.* may be/s/ HAVE_UNISTD_H-0\(.*\) may be/ 1\1 was/" > zconf.temp.h
+  sed < zconf.h "/^#if defined(HAVE_UNISTD_H).* may be/s/ defined.*-0\(.*\) may be/ 1\1 was changed to/" > zconf.temp.h
   mv zconf.temp.h zconf.h
   echo "Checking for unistd.h... Yes." | tee -a configure.log
 else
@@ -665,7 +665,7 @@ cat > $test.c <<EOF
 int main() { return 0; }
 EOF
 if try $CC -c $CFLAGS $test.c; then
-  sed < zconf.h "/^#if HAVE_STDARG_H-0.* may be/s/ HAVE_STDARG_H-0\(.*\) may be/ 1\1 was/" > zconf.temp.h
+  sed < zconf.h "/^#if defined(HAVE_STDARG_H).* may be/s/ defined.*-0\(.*\) may be/ 1\1 was changed to/" > zconf.temp.h
   mv zconf.temp.h zconf.h
   echo "Checking for stdarg.h... Yes." | tee -a configure.log
 else
diff --git a/zconf.h b/zconf.h
index 828ca617e..d12bce47b 100644
--- a/zconf.h
+++ b/zconf.h
@@ -443,11 +443,11 @@ typedef uLong FAR uLongf;
    typedef unsigned long z_crc_t;
 #endif
 
-#if HAVE_UNISTD_H-0     /* may be set to #if 1 by ./configure */
+#if defined(HAVE_UNISTD_H) && HAVE_UNISTD_H-0 /* may be #if 1 after configure */
 #  define Z_HAVE_UNISTD_H
 #endif
 
-#if HAVE_STDARG_H-0     /* may be set to #if 1 by ./configure */
+#if defined(HAVE_STDARG_H) && HAVE_STDARG_H-0 /* may be #if 1 after configure */
 #  define Z_HAVE_STDARG_H
 #endif
 
diff --git a/zconf.h.in b/zconf.h.in
index 828ca617e..d12bce47b 100644
--- a/zconf.h.in
+++ b/zconf.h.in
@@ -443,11 +443,11 @@ typedef uLong FAR uLongf;
    typedef unsigned long z_crc_t;
 #endif
 
-#if HAVE_UNISTD_H-0     /* may be set to #if 1 by ./configure */
+#if defined(HAVE_UNISTD_H) && HAVE_UNISTD_H-0 /* may be #if 1 after configure */
 #  define Z_HAVE_UNISTD_H
 #endif
 
-#if HAVE_STDARG_H-0     /* may be set to #if 1 by ./configure */
+#if defined(HAVE_STDARG_H) && HAVE_STDARG_H-0 /* may be #if 1 after configure */
 #  define Z_HAVE_STDARG_H
 #endif