diff --git a/lib/roken/roken.h b/lib/roken/roken.h
index 7e452591a..1d72b7641 100644
--- a/lib/roken/roken.h
+++ b/lib/roken/roken.h
@@ -30,6 +30,10 @@ char *getusershell(void);
 char * strdup(const char *old);
 #endif
 
+#ifndef HAVE_STRNLEN
+int strnlen(char*, int);
+#endif
+
 #ifndef HAVE_GETDTABLESIZE
 int getdtablesize(void);
 #endif
diff --git a/lib/roken/roken.h.in b/lib/roken/roken.h.in
index 7e452591a..1d72b7641 100644
--- a/lib/roken/roken.h.in
+++ b/lib/roken/roken.h.in
@@ -30,6 +30,10 @@ char *getusershell(void);
 char * strdup(const char *old);
 #endif
 
+#ifndef HAVE_STRNLEN
+int strnlen(char*, int);
+#endif
+
 #ifndef HAVE_GETDTABLESIZE
 int getdtablesize(void);
 #endif