diff --git a/src/common.c b/src/common.c
index 7adbec5..6430a14 100644
--- a/src/common.c
+++ b/src/common.c
@@ -16,3 +16,13 @@ die(char *fmt, ...)
 	va_end(ap);
 	exit(EXIT_FAILURE);
 }
+
+void
+warn(char *fmt, ...)
+{
+	fprintf(stderr, "%s: ", argv0);
+	va_list ap;
+	va_start(ap, fmt);
+	vfprintf(stderr, fmt, ap);
+	va_end(ap);
+}
diff --git a/src/common.h b/src/common.h
index dd46100..6b494cb 100644
--- a/src/common.h
+++ b/src/common.h
@@ -7,6 +7,7 @@
 #define CONFIG_FILE "kiwmi/kiwmirc"
 
 void die(char *fmt, ...);
+void warn(char *fmt, ...);
 
 extern const char *argv0;