diff --git a/registry.cabal b/registry.cabal
--- a/registry.cabal
+++ b/registry.cabal
@@ -4,10 +4,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 6557ba917c4e8ae98b72a5b1b743bccc3d26bef98070e9e3cb45e22a03cbc2a6
+-- hash: af999eb6e06f804acbe70c38692e89b1b97d9dc204f6aecd3f2b716e224380f7
 
 name:           registry
-version:        0.2.0.0
+version:        0.2.0.1
 synopsis:       data structure for assembling components
 description:    This library provides a "Registry" which is a data structure containing a list of functions and values representing dependencies in a directed acyclic graph. A `make` function can then be used to create a value of a specific type out of the registry.
                 You can start with the [README](https://github.com/etorreborre/registry/blob/master/README.md) for a full description of the library.
diff --git a/src/Data/Registry/Registry.hs b/src/Data/Registry/Registry.hs
--- a/src/Data/Registry/Registry.hs
+++ b/src/Data/Registry/Registry.hs
@@ -153,9 +153,14 @@
 
 data ERASED_TYPES
 
+
 -- | In case it is hard to show that the types of 2 registries align
 --   for example with conditional like
---     if True then fun myFunctionWithKnownInputs <: r else r
+--     if True then fun myFunctionWithKnownOutputs <: r else r
+safeCoerce :: (IsSameSet out out1) => Registry ins out -> Registry ins1 out1
+safeCoerce (Registry a b c d) = Registry a b c d
+
+-- | And for extreme cases where you know you're doing the right thing but can't prove it
 unsafeCoerce :: Registry ins out -> Registry ins1 out1
 unsafeCoerce (Registry a b c d) = Registry a b c d
 
diff --git a/src/Data/Registry/Solver.hs b/src/Data/Registry/Solver.hs
--- a/src/Data/Registry/Solver.hs
+++ b/src/Data/Registry/Solver.hs
@@ -52,6 +52,12 @@
 instance IsSubset '[] out t
 instance (CanMake a out t, IsSubset els out t) => IsSubset (a ': els) out t
 
+-- | Compute if each element of a list of types
+--   is the same as another in a different order
+class IsSameSet (types1 :: [Type]) (types2 :: [Type])
+
+instance (ts1 ~ Normalized types1, ts2 ~ Normalized types2, IsSubset ts1 ts2 (), IsSubset ts1 ts2 ()) => IsSameSet types1 types2
+
 -- | Compute if a type is contained in a list of types
 type family Contains (a :: Type) (els :: [Type]) :: Constraint where
   Contains a els = Contains1 a els els
diff --git a/test/Test/Data/Registry/Make/MakeSpec.hs b/test/Test/Data/Registry/Make/MakeSpec.hs
--- a/test/Test/Data/Registry/Make/MakeSpec.hs
+++ b/test/Test/Data/Registry/Make/MakeSpec.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE DataKinds #-}
 {-# OPTIONS_GHC -fno-warn-missing-signatures #-}
 
 module Test.Data.Registry.Make.MakeSpec where
@@ -39,3 +40,24 @@
 -- inverse of add1 (in terms of type signature)
 dda1 :: Text -> Int
 dda1 = T.length
+
+-- test coerce
+r1 = end
+  <: fun dda1
+  <: val ("" :: Text)
+
+r2 :: Registry '[Text] '[Int, Text]
+r2 = normalize $ end
+  <: fun dda1
+  <: val (1 :: Int)
+  <: val ("" :: Text)
+
+r3 :: Registry '[Text, Text, Text] '[Int, Int, Int, Text]
+r3 = fun dda1 <: fun dda1 <: r2
+
+r4 :: Registry '[Text, Text, Text] '[Int, Int, Int, Text]
+r4 =
+   if True then
+     r3
+   else
+     safeCoerce r2