diff --git a/reactive-banana/CHANGELOG.md b/reactive-banana/CHANGELOG.md
index a37c63cf..39c7c16e 100644
--- a/reactive-banana/CHANGELOG.md
+++ b/reactive-banana/CHANGELOG.md
@@ -1,6 +1,12 @@
 Changelog for the `reactive-banana** package
 -------------------------------------------
 
+**unreleased**
+
+* Add `Num`, `Floating`, `Fractional`, and `IsString` instances for `Behavior`. [#34][]
+
+  [#34]: https://github.com/HeinrichApfelmus/reactive-banana/pull/34
+
 **version 1.2.0.0**
 
 * Make `MonadFix` superclass of `MonadMoment`. [#128][]
diff --git a/reactive-banana/src/Reactive/Banana/Combinators.hs b/reactive-banana/src/Reactive/Banana/Combinators.hs
index 82f2bc52..e6caf17c 100644
--- a/reactive-banana/src/Reactive/Banana/Combinators.hs
+++ b/reactive-banana/src/Reactive/Banana/Combinators.hs
@@ -276,20 +276,6 @@ switchB b = liftMoment . M . fmap B . Prim.switchB (unB b) . Prim.mapE (unB) . u
 {-----------------------------------------------------------------------------
     Derived Combinators
 ------------------------------------------------------------------------------}
-{-
-
-Unfortunately, we can't make a  Num  instance because that would
-require  Eq  and  Show .
-
-instance Num a => Num (Behavior t a) where
-    (+) = liftA2 (+)
-    (-) = liftA2 (-)
-    (*) = liftA2 (*)
-    negate = fmap negate
-    abs    = fmap abs
-    signum = fmap signum
-    fromInteger = pure . fromInteger
--}
 infixl 4 <@>, <@
 
 -- | Infix synonym for the 'apply' combinator. Similar to '<*>'.
diff --git a/reactive-banana/src/Reactive/Banana/Types.hs b/reactive-banana/src/Reactive/Banana/Types.hs
index 5a6ef5f1..b02f6e44 100644
--- a/reactive-banana/src/Reactive/Banana/Types.hs
+++ b/reactive-banana/src/Reactive/Banana/Types.hs
@@ -13,6 +13,7 @@ import Control.Applicative
 import Control.Monad
 import Control.Monad.IO.Class
 import Control.Monad.Fix
+import Data.String (IsString(..))
 
 import qualified Reactive.Banana.Internal.Combinators as Prim
 
@@ -93,6 +94,40 @@ instance Applicative Behavior where
 instance Functor Behavior where
     fmap = liftA
 
+instance Num a => Num (Behavior a) where
+    (+) = liftA2 (+)
+    (-) = liftA2 (-)
+    (*) = liftA2 (*)
+    abs = fmap abs
+    signum = fmap signum
+    fromInteger = pure . fromInteger
+    negate = fmap negate
+
+instance Fractional a => Fractional (Behavior a) where
+    (/) = liftA2 (/)
+    fromRational = pure . fromRational
+    recip = fmap recip
+
+instance Floating a => Floating (Behavior a) where
+    (**) = liftA2 (**)
+    acos = fmap acos
+    acosh = fmap acosh
+    asin = fmap asin
+    asinh = fmap asinh
+    atan = fmap atan
+    atanh = fmap atanh
+    cos = fmap cos
+    cosh = fmap cosh
+    exp = fmap exp
+    log = fmap log
+    logBase = liftA2 logBase
+    pi = pure pi
+    sin = fmap sin
+    sinh = fmap sinh
+    sqrt = fmap sqrt
+
+instance IsString a => IsString (Behavior a) where
+    fromString = pure . fromString
 
 -- | The 'Future' monad is just a helper type for the 'changes' function.
 --