diff --git a/configure.ac b/configure.ac
index 7924105..a899b3c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -394,10 +394,44 @@ AC_TRY_COMPILE([#include <sys/socket.h>],
  [ AC_MSG_RESULT(no)]
 )
 
+dnl Check for leveldb, only if explicitly requested
 LEVELDB_CPPFLAGS=
 LIBLEVELDB=
 LIBMEMENV=
-AM_CONDITIONAL([EMBEDDED_LEVELDB],[true])
+AC_ARG_WITH([system-leveldb],
+  [AS_HELP_STRING([--with-system-leveldb],
+  [Build with system LevelDB (default is no; DANGEROUS; NOT SUPPORTED)])],
+  [system_leveldb=$withval],
+  [system_leveldb=no]
+)
+if test x$system_leveldb != xno; then
+  LEVELDB_CPPFLAGS=
+  AC_CHECK_LIB([leveldb],[main],[
+    LIBLEVELDB=-lleveldb
+  ],[
+    AC_MSG_ERROR([leveldb library not found; using --with-system-leveldb is not supported anyway])
+  ])
+  TEMP_LIBS="$LIBS"
+  LIBS="$LIBS $LIBLEVELDB"
+  AC_CHECK_LIB([memenv],[main],[
+    LIBMEMENV=-lmemenv
+  ],[
+    AC_MSG_ERROR([LevelDB's memenv library not found; using --with-system-leveldb is not supported anyway])
+  ])
+  LIBS="$TEMP_LIBS"
+  AC_CHECK_HEADER([leveldb/filter_policy.h],[],[
+    AC_MSG_ERROR([LevelDB headers not found; using --with-system-leveldb is not supported anyway])
+  ])
+  AC_CHECK_HEADER([leveldb/helpers/memenv.h],[
+    AC_MSG_CHECKING([for memenv.h path])
+    BITCOIN_SUBDIR_TO_INCLUDE([LEVELDB_CPPFLAGS],[leveldb/helpers/],[memenv])
+  ],[
+    AC_CHECK_HEADER([memenv.h],[],[
+      AC_MSG_ERROR([LevelDB headers not found; using --with-system-leveldb is not supported anyway])
+    ])
+  ])
+fi
+AM_CONDITIONAL([EMBEDDED_LEVELDB],[test x$system_leveldb = xno])
 AC_SUBST(LEVELDB_CPPFLAGS)
 AC_SUBST(LIBLEVELDB)
 AC_SUBST(LIBMEMENV)
diff --git a/src/m4/bitcoin_subdir_to_include.m4 b/src/m4/bitcoin_subdir_to_include.m4
index 66f106c..5f0a3b1 100644
--- a/src/m4/bitcoin_subdir_to_include.m4
+++ b/src/m4/bitcoin_subdir_to_include.m4
@@ -5,7 +5,7 @@ AC_DEFUN([BITCOIN_SUBDIR_TO_INCLUDE],[
     AC_MSG_RESULT([default])
   else
     echo "#include <$2$3.h>" >conftest.cpp
-    newinclpath=`${CXXCPP} ${CPPFLAGS} -M conftest.cpp 2>/dev/null | [ tr -d '\\n\\r\\\\' | sed -e 's/^.*[[:space:]:]\(\/[^[:space:]]*\)]$3[\.h[[:space:]].*$/\1/' -e t -e d`]
+    newinclpath=$(${CXXCPP} ${CPPFLAGS} -M conftest.cpp 2>/dev/null | sed [-E -e ':a' -e '/\\$/!b b' -e N -e 's/\\\n/ /' -e 't a' -e ':b' -e 's/^[^:]*:[[:space:]]*(([^[:space:]\]|\\.)*[[:space:]])*(([^[:space:]\]|\\.)*)]$3\.h[([[:space:]].*)?$/\3/' -e 't' -e d])
     AC_MSG_RESULT([${newinclpath}])
     if test "x${newinclpath}" != "x"; then
       eval "$1=\"\$$1\"' -I${newinclpath}'"