diff --git a/src/lib/Math/Bezier/Cubic.hs b/src/lib/Math/Bezier/Cubic.hs
index 9181e7c..d7185e2 100644
--- a/src/lib/Math/Bezier/Cubic.hs
+++ b/src/lib/Math/Bezier/Cubic.hs
@@ -177,7 +177,7 @@ ddist ( Bezier {..} ) c = [ a5, a4, a3, a2, a1, a0 ]
 
 -- | Finds the closest point to a given point on a cubic Bézier curve.
 closestPoint
-  :: forall v r p. ( Torsor v p, Inner r v, RealFloat r, Prim r )
+  :: forall v r p. ( Torsor v p, Inner r v, RealFloat r, Prim r, NFData r )
   => Bezier p -> p -> ArgMin r ( r, p )
 closestPoint pts c = pickClosest ( 0 :| 1 : roots ) -- todo: also include the self-intersection point if one exists
   where
diff --git a/src/lib/Math/Bezier/Quadratic.hs b/src/lib/Math/Bezier/Quadratic.hs
index de37dd9..1d634c1 100644
--- a/src/lib/Math/Bezier/Quadratic.hs
+++ b/src/lib/Math/Bezier/Quadratic.hs
@@ -145,7 +145,7 @@ ddist ( Bezier {..} ) c = [ a3, a2, a1, a0 ]
 
 -- | Finds the closest point to a given point on a quadratic Bézier curve.
 closestPoint
-  :: forall v r p. ( Torsor v p, Inner r v, RealFloat r, Prim r )
+  :: forall v r p. ( Torsor v p, Inner r v, RealFloat r, Prim r, NFData r )
   => Bezier p -> p -> ArgMin r ( r, p )
 closestPoint pts c = pickClosest ( 0 :| 1 : roots )
   where
diff --git a/src/lib/Math/Bezier/Stroke.hs b/src/lib/Math/Bezier/Stroke.hs
index f1233da..b7c6a29 100644
--- a/src/lib/Math/Bezier/Stroke.hs
+++ b/src/lib/Math/Bezier/Stroke.hs
@@ -161,7 +161,7 @@ discardCache ( view ( typed @( CachedStroke s ) ) -> CachedStroke { cachedStroke
 
 {-# INLINE invalidateCache #-}
 invalidateCache :: forall crvData. HasType ( CachedStroke RealWorld ) crvData => crvData -> crvData
-invalidateCache = runRW# \ s -> do
+invalidateCache = runRW# \ s ->
   case newMutVar# Nothing s of
     (# _, mutVar #) ->
       set ( typed @( CachedStroke RealWorld ) )
diff --git a/src/lib/Math/Roots.hs b/src/lib/Math/Roots.hs
index 0cebab4..08a0d7b 100644
--- a/src/lib/Math/Roots.hs
+++ b/src/lib/Math/Roots.hs
@@ -6,8 +6,6 @@
 {-# LANGUAGE ScopedTypeVariables   #-}
 {-# LANGUAGE TypeApplications      #-}
 
-{-# OPTIONS_GHC -fno-warn-partial-type-signatures #-}
-
 module Math.Roots where
 
 -- base
@@ -20,6 +18,10 @@ import Data.Complex
 import Data.Maybe
   ( mapMaybe )
 
+-- deepseq
+import Control.DeepSeq
+  ( NFData, force )
+
 -- primitive
 import Control.Monad.Primitive
   ( PrimMonad(PrimState) )
@@ -70,7 +72,7 @@ solveQuadratic a0 a1 a2
 --
 -- Coefficients are given in order of decreasing degree, e.g.:
 --  x² + 7 is given by [ 1, 0, 7 ].
-realRoots :: forall a. ( RealFloat a, Prim a ) => Int -> [ a ] -> [ a ]
+realRoots :: forall a. ( RealFloat a, Prim a, NFData a ) => Int -> [ a ] -> [ a ]
 realRoots maxIters coeffs = mapMaybe isReal ( roots epsilon maxIters ( map (:+ 0) coeffs ) )
   where
     isReal :: Complex a -> Maybe a
@@ -84,18 +86,18 @@ realRoots maxIters coeffs = mapMaybe isReal ( roots epsilon maxIters ( map (:+ 0
 --
 -- N.B. The forward deflation process is only guaranteed to be numerically stable
 -- if Laguerre's method finds roots in increasing order of magnitude.
-roots :: forall a. ( RealFloat a, Prim a ) => a -> Int -> [ Complex a ] -> [ Complex a ]
+roots :: forall a. ( RealFloat a, Prim a, NFData a ) => a -> Int -> [ Complex a ] -> [ Complex a ]
 roots eps maxIters coeffs = runST do
   let
     coeffPrimArray :: PrimArray ( Complex a )
     coeffPrimArray = primArrayFromList coeffs
     sz :: Int
     sz = sizeofPrimArray coeffPrimArray
-  p <- unsafeThawPrimArray coeffPrimArray
+  ( p :: MutablePrimArray s ( Complex a ) ) <- unsafeThawPrimArray coeffPrimArray
   let
-    go :: Int -> [ Complex a ] -> ST _s [ Complex a ]
-    go i rs = do
-      !r <- laguerre eps maxIters p 0 -- Start Laguerre's method at 0 for best chance of numerical stability.
+    go :: Int -> [ Complex a ] -> ST s [ Complex a ]
+    go !i rs = do
+      !r <- force <$> laguerre eps maxIters p 0 -- Start Laguerre's method at 0 for best chance of numerical stability.
       if i <= 2
       then pure ( r : rs )
       else do
@@ -116,7 +118,7 @@ deflate r p = do
       shrinkMutablePrimArray p deg
       let
         go :: a -> Int -> m ()
-        go b i = unless ( i >= deg ) do
+        go !b !i = unless ( i >= deg ) do
           ai <- readPrimArray p i
           writePrimArray p i ( ai + r * b )
           go ai ( i + 1 )
@@ -137,7 +139,7 @@ laguerre eps maxIters p x0 = do
   p'' <- derivative p'
   let
     go :: Int -> Complex a -> m ( Complex a )
-    go iterationsLeft x = do
+    go !iterationsLeft !x = do
       x' <- laguerreStep eps p p' p'' x
       if iterationsLeft <= 1 || magnitude ( x' - x ) < eps
       then pure x'
@@ -189,11 +191,12 @@ eval p x = do
   n <- getSizeofMutablePrimArray p
   let
     go :: a -> Int -> m a
-    go !a i =
-      if i >= n
-      then pure a
-      else do
-        !b <- readPrimArray p i
+    go !a !i
+      | i >= n
+      = pure a
+      | otherwise
+      = do
+        b <- readPrimArray p i
         go ( b + x * a ) ( i + 1 )
   an <- readPrimArray p 0
   go an 1
@@ -208,8 +211,9 @@ derivative p = do
   p' <- cloneMutablePrimArray p 0 deg
   let
     go :: Int -> m ()
-    go i = unless ( i >= deg ) do
+    go !i = unless ( i >= deg - 1 ) do
       a <- readPrimArray p' i
       writePrimArray p' i ( a * fromIntegral ( deg - i ) )
+      go ( i + 1 )
   go 0
   pure p'