Can't infer constraint of pattern synonyms

Can't infer constraint of:

-- pattern Real' :: Num a => a -> Complex a
pattern Real' r <- r :+ _
  where Real' r =  r :+ 0

teR4.hs:12:25: error: …
    • No instance for (Num t) arising from the literal ‘0’
      Possible fix:                        
        add (Num t) to the context of
          the type signature for:    
            Main.$bReal' :: t -> Complex t
    • In the second argument of ‘(:+)’, namely ‘0’
      In the expression: r :+ 0
      In an equation for ‘$bReal'’: $bReal' r = r :+ 0
Compilation failed.

Should it be able to?

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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