diff --git a/configure.ac b/configure.ac
index 23d820e..e4d6aa4 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1278,7 +1278,11 @@ if test X"$OPT_SSL" != Xno; then
 
   dnl we're done using pkg-config for openssl
   PKG_CONFIG_LIBDIR="$SAVE_PKG_CONFIG_LIBDIR"
-  export PKG_CONFIG_LIBDIR
+  if test -z "$PKG_CONFIG_LIBDIR"; then
+    unset PKG_CONFIG_LIBDIR
+  else
+    export PKG_CONFIG_LIBDIR
+  fi
 
   dnl finally, set flags to use SSL
   CPPFLAGS="$CPPFLAGS $SSL_CPPFLAGS"