diff --git a/src/broker.jl b/src/broker.jl
index 9094549..7afb94d 100644
--- a/src/broker.jl
+++ b/src/broker.jl
@@ -291,6 +291,7 @@ function verify_signature(twin, msg)
         hash = MbedTLS.digest(MD_SHA256, plain)
         MbedTLS.verify(ctx, MD_SHA256, hash, msg.signature)
     catch e
+        @info "verify signature: $e ($(typeof(e)))"
         if isa(e, MbedTLS.MbedException) &&
            e.ret == MbedTLS.MBEDTLS_ERR_RSA_VERIFY_FAILED
             rethrow()