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