--- vorbis.m4
+++ vorbis.m4
@@ -19,7 +19,7 @@
     VORBIS_LIBS="-L$vorbis_libraries"
   elif test "x$vorbis_prefix" != "x" ; then
     VORBIS_LIBS="-L$vorbis_prefix/lib"
-  elif test "x$prefix" != "xNONE"; then
+  elif test "x$prefix" != "xNONE" -a "x$prefix" != "x/usr"; then
     VORBIS_LIBS="-L$prefix/lib"
   fi
 
@@ -31,7 +31,7 @@
     VORBIS_CFLAGS="-I$vorbis_includes"
   elif test "x$vorbis_prefix" != "x" ; then
     VORBIS_CFLAGS="-I$vorbis_prefix/include"
-  elif test "x$prefix" != "xNONE"; then
+  elif test "x$prefix" != "xNONE" -a "x$prefix" != "x/usr"; then
     VORBIS_CFLAGS="-I$prefix/include"
   fi