diff --git a/output.c b/output.c
index 7cab383..18f9cf0 100644
--- a/output.c
+++ b/output.c
@@ -598,6 +598,9 @@ frame_callback (Dwfl_Frame *state, void *arg)
 					   NULL, NULL, NULL);
 		symname = dwfl_module_addrinfo(mod, pc, &off, &sym,
 					       NULL, NULL, NULL);
+	} else {
+		modname = "unknown";
+		symname = "unknown";
 	}
 
 	/* This mimics the output produced by libunwind below.  */