diff --git a/Math/VectorSpace/Docile.hs b/Math/VectorSpace/Docile.hs
--- a/Math/VectorSpace/Docile.hs
+++ b/Math/VectorSpace/Docile.hs
@@ -65,9 +65,11 @@
 
 import Numeric.IEEE
 
+import Data.CallStack
 
 
 
+
 -- | 'SemiInner' is the class of vector spaces with finite subspaces in which
 --   you can define a basis that can be used to project from the whole space
 --   into the subspace. The usual application is for using a kind of
@@ -246,16 +248,25 @@
               [] -> StateT $ const Nothing
               (b:bs') -> put bs' >> return (f a b)
 
-embedFreeSubspace :: ∀ v t r . (SemiInner v, RealFrac' (Scalar v), Hask.Traversable t)
+embedFreeSubspace :: ∀ v t r . (HasCallStack, SemiInner v, RealFrac' (Scalar v), Hask.Traversable t)
             => t v -> Maybe (ReifiedLens' v (t (Scalar v)))
 embedFreeSubspace vs = fmap (\(g,s) -> Lens (lens g s)) result
  where vsList = toList vs
        result = fmap (genGet&&&genSet) . sequenceA $ dualBasis vsList
        genGet vsDuals u = case zipTravWith (\_v dv -> dv<.>^u) vs vsDuals of
                 Just cs -> cs
+                Nothing -> error $ "Cannot map into free subspace using a set of "
+                                 ++ show (length vsList)
+                                 ++ " vectors and " ++ show (length vsDuals)
+                                 ++ " dual vectors."
        genSet vsDuals u coefs = case zipTravWith (,) coefs $ zip vsList vsDuals of
                 Just updators -> foldl' (\ur (c,(v,v')) -> ur ^+^ v^*(c - v'<.>^ur))
                                         u updators
+                Nothing -> error $ "Cannot map from free subspace using a set of "
+                                 ++ show (length vsList)
+                                 ++ " vectors, " ++ show (length vsDuals)
+                                 ++ " dual vectors and "
+                                 ++ show (length coefs) ++ " coefficients."
 
 
 instance SemiInner ℝ where
diff --git a/linearmap-category.cabal b/linearmap-category.cabal
--- a/linearmap-category.cabal
+++ b/linearmap-category.cabal
@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                linearmap-category
-version:             0.3.4.0
+version:             0.3.5.0
 synopsis:            Native, complete, matrix-free linear algebra.
 description:         The term /numerical linear algebra/ is often used almost
                      synonymous with /matrix modifications/. However, what's interesting
@@ -48,14 +48,15 @@
                        Math.VectorSpace.Docile
   other-extensions:    FlexibleInstances, UndecidableInstances, FunctionalDependencies, TypeOperators, TypeFamilies
   build-depends:       base >=4.8 && <5,
-                       vector-space >=0.11 && <0.12,
+                       vector-space >=0.11 && <0.13,
                        constrained-categories >=0.3 && <0.4,
                        containers, vector,
                        tagged,
                        free-vector-spaces >= 0.1.4 && < 0.2,
                        linear, lens, transformers,
-                       manifolds-core >= 0.4.4 && < 0.5,
+                       manifolds-core >= 0.4.4 && < 0.6,
                        semigroups,
-                       ieee754 >= 0.7 && < 0.9
+                       ieee754 >= 0.7 && < 0.9,
+                       call-stack
   -- hs-source-dirs:      
   default-language:    Haskell2010