diff --git a/expand.c b/expand.c
index 6c453fd..60c5623 100644
--- a/expand.c
+++ b/expand.c
@@ -74,18 +74,18 @@ expand(const char *file, FILE *fp, int tabstop)
 			if (col)
 				col--;
 			bol = 0;
-			writerune(&r);
+			writerune("<stdout>", stdout, &r);
 			break;
 		case '\n':
 			col = 0;
 			bol = 1;
-			writerune(&r);
+			writerune("<stdout>", stdout, &r);
 			break;
 		default:
 			col++;
 			if (r != ' ')
 				bol = 0;
-			writerune(&r);
+			writerune("<stdout>", stdout, &r);
 			break;
 		}
 	}
diff --git a/libutf/writerune.c b/libutf/writerune.c
index 0615860..eb9cfac 100644
--- a/libutf/writerune.c
+++ b/libutf/writerune.c
@@ -7,16 +7,16 @@
 #include "../utf.h"
 
 void
-writerune(Rune *r)
+writerune(const char *file, FILE *fp, Rune *r)
 {
 	char buf[UTFmax];
 	int n;
 
 	if ((n = runetochar(buf, r)) > 0) {
-		fwrite(buf, n, 1, stdout);
-		if (ferror(stdout)) {
-			fprintf(stderr, "stdout: write error: %s\n",
-				strerror(errno));
+		fwrite(buf, n, 1, fp);
+		if (ferror(fp)) {
+			fprintf(stderr, "%s: write error: %s\n",
+				file, strerror(errno));
 			exit(1);
 		}
 	}
diff --git a/utf.h b/utf.h
index 44c5bba..26b9a6f 100644
--- a/utf.h
+++ b/utf.h
@@ -50,4 +50,4 @@ int isupperrune(Rune);
 int isdigitrune(Rune);
 
 int readrune(const char *, FILE *, Rune *);
-void writerune(Rune *);
+void writerune(const char *, FILE *, Rune *);