diff --git a/src/auto/configure b/src/auto/configure
index fba6a19..4f43632 100755
--- a/src/auto/configure
+++ b/src/auto/configure
@@ -14960,6 +14960,10 @@
   fi
 fi
 
+if `echo "$CFLAGS" | grep -v D_XEENTRANT >/dev/null`; then
+  CFLAGS="$CFLAGS -D_REENTRANT"
+fi
+
 DEPEND_CFLAGS_FILTER=
 if test "$GCC" = yes; then
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for GCC 3 or later" >&5
diff --git a/src/configure.ac b/src/configure.ac
index 5ec9557..4cd6dea 100644
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -4504,6 +4504,12 @@
   fi
 fi
 
+dnl On some systems REENTRANT needs to be defined.  It should not hurt to use
+dnl it everywhere.
+if `echo "$CFLAGS" | grep -v D_REENTRANT >/dev/null`; then
+  CFLAGS="$CFLAGS -D_REENTRANT"
+fi
+
 dnl gcc 3.1 changed the meaning of -MM.  The only solution appears to be to
 dnl use "-isystem" instead of "-I" for all non-Vim include dirs.
 dnl But only when making dependencies, cproto and lint don't take "-isystem".
diff --git a/src/version.c b/src/version.c
index 742f899..d56e443 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3406,
+/**/
     3405,
 /**/
     3404,