diff --git a/interpolator.cabal b/interpolator.cabal
--- a/interpolator.cabal
+++ b/interpolator.cabal
@@ -1,16 +1,16 @@
 cabal-version: 1.12
 
--- This file has been generated from package.yaml by hpack version 0.31.0.
+-- This file has been generated from package.yaml by hpack version 0.31.2.
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 81768ccb2307e3de44aa6d39b0295cc9a459e02c136be78538dc08541f68365e
+-- hash: 99eadf3b4df4c6738c42e6f6e4789426dc11140f7faae6ecb7253fc6017283a2
 
 name:           interpolator
-version:        0.1.1
+version:        0.1.2
 synopsis:       Runtime interpolation of environment variables in records using profunctors
 description:    Runtime interpolation of environment variables in records using profunctors. See
-                `https://github.com/tvision-insights/interpolator/README.md`.
+                the [README](https://github.com/tvision-insights/interpolator/blob/master/README.md).
 category:       Data
 stability:      experimental
 homepage:       https://github.com/tvision-insights/interpolator
diff --git a/src/Data/Interpolation.hs b/src/Data/Interpolation.hs
--- a/src/Data/Interpolation.hs
+++ b/src/Data/Interpolation.hs
@@ -6,6 +6,7 @@
 import Control.Monad.IO.Class (MonadIO, liftIO)
 import Control.Monad.Reader (Reader, asks, runReader)
 import Data.Aeson (FromJSON, ToJSON, Value (String), parseJSON, toJSON, withText)
+import Data.Char (isAlphaNum)
 import Data.Containers (mapFromList, setFromList, setToList)
 import Data.Either.Validation (Validation (Failure, Success), validationToEither)
 import Data.Map (Map, lookup)
@@ -186,12 +187,12 @@
 maybeGen :: Gen a -> Gen (Maybe a)
 maybeGen x = frequency [(1, pure Nothing), (3, Just <$> x)]
 
-noEnv, noColons :: Gen T.Text
+noEnv, varNameAllowed :: Gen T.Text
 noEnv = fmap T.pack $ arbitrary `suchThat` (\ s -> not ("_env:" `isPrefixOf` s) && not (null s))
-noColons = fmap T.pack . listOf1 $ arbitrary `suchThat` (/= ':')
+varNameAllowed = fmap T.pack . listOf1 $ arbitrary `suchThat` (\c -> isAlphaNum c || c == '_')
 
 instance Arbitrary TemplateKey where
-  arbitrary = TemplateKey <$> noColons
+  arbitrary = TemplateKey <$> varNameAllowed
 
 instance {-# OVERLAPPABLE #-} Arbitrary a => Arbitrary (Uninterpolated a) where
   arbitrary = oneof
@@ -202,5 +203,5 @@
 instance {-# OVERLAPPING #-} Arbitrary (Uninterpolated T.Text) where
   arbitrary = oneof
     [ Literal <$> noEnv
-    , Templated <$> (Template <$> arbitrary <*> maybeGen noColons)
+    , Templated <$> (Template <$> arbitrary <*> maybeGen noEnv)
     ]