diff --git a/lib/roken/err.h b/lib/roken/err.h
index 473b42071..79b8dea42 100644
--- a/lib/roken/err.h
+++ b/lib/roken/err.h
@@ -9,7 +9,7 @@
 #include <string.h>
 #include <stdarg.h>
 
-extern char *__progname;
+extern const char *__progname;
 
 #ifndef __GNUC__
 #define __attribute__(x)
diff --git a/lib/roken/err.hin b/lib/roken/err.hin
index 473b42071..79b8dea42 100644
--- a/lib/roken/err.hin
+++ b/lib/roken/err.hin
@@ -9,7 +9,7 @@
 #include <string.h>
 #include <stdarg.h>
 
-extern char *__progname;
+extern const char *__progname;
 
 #ifndef __GNUC__
 #define __attribute__(x)