diff --git a/util/concat.c b/util/concat.c
index 939219d..a276fbb 100644
--- a/util/concat.c
+++ b/util/concat.c
@@ -1,5 +1,6 @@
 /* See LICENSE file for copyright and license details. */
 #include <stdio.h>
+#include <unistd.h>
 
 #include "../text.h"
 #include "../util.h"
@@ -8,14 +9,12 @@ void
 concat(FILE *fp1, const char *s1, FILE *fp2, const char *s2)
 {
 	char buf[BUFSIZ];
-	size_t n;
+	ssize_t n;
 
-	while ((n = fread(buf, 1, sizeof buf, fp1)) > 0) {
-		if (fwrite(buf, 1, n, fp2) != n)
+	while ((n = read(fileno(fp1), buf, sizeof buf)) > 0) {
+		if (write(fileno(fp2), buf, n) != n)
 			eprintf("%s: write error:", s2);
-		if (feof(fp1))
-			break;
 	}
-	if (ferror(fp1))
+	if (n < 0)
 		eprintf("%s: read error:", s1);
 }