diff --git a/usr.sbin/config/configvers.h b/usr.sbin/config/configvers.h
--- a/usr.sbin/config/configvers.h
+++ b/usr.sbin/config/configvers.h
@@ -49,7 +49,7 @@
  *
  * $FreeBSD$
  */
-#define	CONFIGVERS	600019
+#define	CONFIGVERS	600020
 #define	MAJOR_VERS(x)	((x) / 100000)
 
 /* Last config(8) version to require envmode/hintmode */
diff --git a/usr.sbin/config/mkmakefile.c b/usr.sbin/config/mkmakefile.c
--- a/usr.sbin/config/mkmakefile.c
+++ b/usr.sbin/config/mkmakefile.c
@@ -71,6 +71,15 @@
 
 static const char keywords[] = { "!|()" };
 
+struct files;
+typedef STAILQ_HEAD(,files) files_head_t;
+typedef STAILQ_ENTRY(files) files_entry_t;
+
+struct files {
+	files_entry_t entry;
+	char *this;
+};
+
 static void errout(const char *fmt, ...)
 {
 	va_list ap;
@@ -96,6 +105,38 @@
 	return (0);
 }
 
+/*
+ * Add new file entry.
+ */
+static char *
+fe_new(const char *fname, files_head_t *phead)
+{
+	struct files *pfe;
+
+	pfe = malloc(sizeof(*pfe));
+	pfe->this = ns(fname);
+	STAILQ_INSERT_TAIL(phead, pfe, entry);
+	return (pfe->this);
+}
+
+/*
+ * Remove file entry.
+ */
+static char *
+fe_get(files_head_t *phead)
+{
+	struct files *pfe;
+	char *retval;
+
+	pfe = STAILQ_FIRST(phead);
+	if (pfe == NULL)
+		return (NULL);
+	STAILQ_REMOVE_HEAD(phead, entry);
+	retval = pfe->this;
+	free(pfe);
+	return (retval);
+}
+
 /*
  * Make a new file list entry
  */
@@ -392,12 +433,13 @@
 read_file(char *fname)
 {
 	char ifname[MAXPATHLEN];
-	FILE *fp;
+	files_head_t fhead;
 	struct file_list *tp;
+	FILE *fp;
 	struct device *dp;
 	struct opt *op;
 	char *wd, *this, *compilewith, *depends, *clean, *warning;
-	const char *objprefix;
+	char *objprefix;
 	int level;
 	int filetype;
 	bool std;
@@ -414,8 +456,11 @@
 	fp = fopen(fname, "r");
 	if (fp == NULL)
 		err(1, "%s", fname);
+
+	STAILQ_INIT(&fhead);
 next:
 	/*
+	 * # this is a comment
 	 * include "filename"
 	 * filename    [ standard | optional ]
 	 *	[ dev* [ | dev* ... ] | [ no-obj ]
@@ -452,13 +497,19 @@
 			;
 		goto next;
 	}
-	this = ns(wd);
+nextfile:
+	this = fe_new(wd, &fhead);
 	wd = get_word(fp, keywords);
 	if (wd == (char *)EOF)
 		return;
 	if (wd == NULL)
 		errout("%s: No type for %s.\n", fname, this);
-	tp = fl_lookup(this);
+	if (eq(wd, "|")) {
+		wd = get_word(fp, NULL);
+		if (wd == (char *)EOF || wd == NULL)
+			errout("%s: No additional filename after %s.\n", fname, this);
+		goto nextfile;
+	}
 	level = 0;
 	/* reset logic state */
 	compile[level] = false;
@@ -476,7 +527,7 @@
 	before_depend = false;
 	nowerror = false;
 	filetype = NORMAL;
-	objprefix = "";
+	objprefix = NULL;
 	if (eq(wd, "standard"))
 		std = true;
 	else if (!eq(wd, "optional"))
@@ -624,32 +675,49 @@
 		errout("%s: unbalanced use of parenthesis\n",
 		    fname);
 	compile[level] |= match[level];
-	if (compile[level] && tp == NULL) {
+	if (compile[level]) {
 		if (std == false && anyreqs[level] == false)
 			errout("%s: what is %s optional on?\n",
 			       fname, this);
-		tp = new_fent();
-		tp->f_fn = this;
-		tp->f_type = filetype;
-		if (filetype == LOCAL)
-			tp->f_srcprefix = "";
-		else
-			tp->f_srcprefix = "$S/";
-		if (imp_rule)
-			tp->f_flags |= NO_IMPLCT_RULE;
-		if (no_ctfconvert)
-			tp->f_flags |= NO_CTFCONVERT;
-		if (no_obj)
-			tp->f_flags |= NO_OBJ | NO_CTFCONVERT;
-		if (before_depend)
-			tp->f_flags |= BEFORE_DEPEND;
-		if (nowerror)
-			tp->f_flags |= NOWERROR;
-		tp->f_compilewith = compilewith;
-		tp->f_depends = depends;
-		tp->f_clean = clean;
-		tp->f_warn = warning;
-		tp->f_objprefix = objprefix;
+
+		while ((this = fe_get(&fhead)) != NULL) {
+			if (fl_lookup(this) != NULL) {
+				fprintf(stderr, "WARNING: %s is enabled more than once. Ignored line from %s\n", this, fname);
+				free(this);
+				continue;
+			}
+			tp = new_fent();
+			tp->f_fn = this;
+			tp->f_type = filetype;
+			if (filetype == LOCAL)
+				tp->f_srcprefix = "";
+			else
+				tp->f_srcprefix = "$S/";
+			if (imp_rule)
+				tp->f_flags |= NO_IMPLCT_RULE;
+			if (no_ctfconvert)
+				tp->f_flags |= NO_CTFCONVERT;
+			if (no_obj)
+				tp->f_flags |= NO_OBJ | NO_CTFCONVERT;
+			if (before_depend)
+				tp->f_flags |= BEFORE_DEPEND;
+			if (nowerror)
+				tp->f_flags |= NOWERROR;
+			tp->f_compilewith = compilewith;
+			tp->f_depends = depends;
+			tp->f_clean = clean;
+			tp->f_warn = warning;
+			tp->f_objprefix = objprefix ? objprefix : "";
+		}
+	} else {
+		free(compilewith);
+		free(depends);
+		free(clean);
+		free(warning);
+		free(objprefix);
+
+		while ((this = fe_get(&fhead)) != NULL)
+			free(this);
 	}
 	goto next;
 }