diff --git a/configure.ac b/configure.ac
index 7cbd40922..7ea6039c3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -23,33 +23,41 @@ case "$CC" in
 	;;
 esac
 
-local_lib=
-local_include=
+if test -z "$prefix" || test "x$prefix" = xNONE; then
+	local_lib=
+	local_include=
 
-# aren't autotools supposed to be smart enough to figure this out?
-# oh well, the git-core Makefile managed to do some of the work for us :)
-case "$host_os" in
-darwin*)
-	local_lib='/sw/lib /opt/local/lib'
-	local_include='/sw/include /opt/local/include'
-	;;
-freebsd* | openbsd*)
-	local_lib=/usr/local/lib
-	local_include=/usr/local/include
-	;;
-netbsd*)
-	local_lib=/usr/pkg/lib
-	local_include=/usr/pkg/include
-	LDFLAGS="$LDFLAGS -Wl,-rpath,/usr/pkg/lib"
-	;;
-esac
+	# aren't autotools supposed to be smart enough to figure this out?  oh
+	# well, the git-core Makefile managed to do some of the work for us :)
+	case "$host_os" in
+	darwin*)
+		local_lib='/sw/lib /opt/local/lib'
+		local_include='/sw/include /opt/local/include'
+		;;
+	freebsd* | openbsd*)
+		local_lib=/usr/local/lib
+		local_include=/usr/local/include
+		;;
+	netbsd*)
+		local_lib=/usr/pkg/lib
+		local_include=/usr/pkg/include
+		LDFLAGS="$LDFLAGS -Wl,-rpath,/usr/pkg/lib"
+		;;
+	esac
 
-for d in $local_lib; do
-	test -d "$d" && LDFLAGS="$LDFLAGS -L$d"
-done
-for d in $local_include; do
-	test -d "$d" && CFLAGS="$CFLAGS -I$d"
-done
+	for d in $local_lib; do
+		if test -d "$d"; then
+			LDFLAGS="$LDFLAGS -L$d"
+			break
+		fi
+	done
+	for d in $local_include; do
+		if test -d "$d"; then
+			CFLAGS="$CFLAGS -I$d"
+			break
+		fi
+	done
+fi
 
 AC_ARG_ENABLE(ao,[  --enable-ao             enable support for libao (default: disable)],[enable_ao=$enableval],[enable_ao=no])
 AC_ARG_ENABLE(shout,[  --disable-shout         disable support for streaming through shout (default: enable)],[enable_shout=$enableval],[enable_shout=yes])