diff --git a/acconfig.h b/acconfig.h
index 97b96f8..6ae4eab 100644
--- a/acconfig.h
+++ b/acconfig.h
@@ -5,4 +5,5 @@
 #undef PHYSFS_SUPPORTS_ZIP
 #undef PHYSFS_SUPPORTS_GRP
 #undef PHYSFS_HAVE_READLINE
+#undef PHYSFS_HAVE_LLSEEK
 
diff --git a/configure.in b/configure.in
index e57983c..b7e736a 100644
--- a/configure.in
+++ b/configure.in
@@ -93,6 +93,13 @@ dnl ---------------------------------------------------------------------
 dnl Checks for libraries.
 dnl ---------------------------------------------------------------------
 
+dnl !!! FIXME: Not sure how to detect this...
+dnl check for 64-bit llseek()...
+dnl AC_CHECK_LIB(c, llseek, have_llseek=yes)
+if test x$have_llseek = xyes; then
+  AC_DEFINE(PHYSFS_HAVE_LLSEEK)
+fi
+
 require_zlib="no"
 
 dnl Check for zip archiver inclusion...