diff --git a/aeson-typescript.cabal b/aeson-typescript.cabal
--- a/aeson-typescript.cabal
+++ b/aeson-typescript.cabal
@@ -2,10 +2,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: b86c36fc20ac6e32d044e63a6caa18dddf3941b36e79c3028a3a7f6ba2013073
+-- hash: 642ba0d728cb3be28a4296b85b360f01995570c1a66ec3a36bfb1432d2095f58
 
 name:           aeson-typescript
-version:        0.1.0.2
+version:        0.1.0.3
 synopsis:       Generate TypeScript definition files from your ADTs
 description:    Please see the README on Github at <https://github.com/codedownio/aeson-typescript#readme>
 category:       Text, Web, JSON
@@ -23,6 +23,7 @@
 extra-source-files:
     ChangeLog.md
     README.md
+    test/assets/npm_install.sh
     test/assets/package.json
     test/assets/yarn.lock
     test/assets/yarn_install.sh
diff --git a/src/Data/Aeson/TypeScript/Instances.hs b/src/Data/Aeson/TypeScript/Instances.hs
--- a/src/Data/Aeson/TypeScript/Instances.hs
+++ b/src/Data/Aeson/TypeScript/Instances.hs
@@ -38,6 +38,12 @@
 instance TypeScript Integer where
   getTypeScriptType _ = "number"
 
+instance TypeScript Float where
+  getTypeScriptType _ = "number"
+
+instance TypeScript Double where
+  getTypeScriptType _ = "number"
+
 instance TypeScript Bool where
   getTypeScriptType _ = "boolean"
 
diff --git a/src/Data/Aeson/TypeScript/TH.hs b/src/Data/Aeson/TypeScript/TH.hs
--- a/src/Data/Aeson/TypeScript/TH.hs
+++ b/src/Data/Aeson/TypeScript/TH.hs
@@ -80,6 +80,7 @@
   module Data.Aeson.TypeScript.Instances
   ) where
 
+import Control.Monad
 import Data.Aeson as A
 import Data.Aeson.TypeScript.Formatting
 import Data.Aeson.TypeScript.Instances ()
@@ -150,6 +151,8 @@
 deriveTypeScript options name = do
   datatypeInfo@(DatatypeInfo {..}) <- reifyDatatype name
 
+  assertExtensionsTurnedOn datatypeInfo
+
   let getFreeVariableName (SigT (VarT name) kind) = Just name
       getFreeVariableName typ = Nothing
 
@@ -332,6 +335,19 @@
 getTagSingleConstructors options = tagSingleConstructors options
 #else
 getTagSingleConstructors options = False
+#endif
+
+-- Between Template Haskell 2.10 and 2.11, the ability to look up which extensions are turned on was added
+assertExtensionsTurnedOn :: DatatypeInfo -> Q ()
+#if MIN_VERSION_template_haskell(2,11,0)
+assertExtensionsTurnedOn (DatatypeInfo {..}) = do
+  -- Check that necessary language extensions are turned on
+  scopedTypeVariablesEnabled <- isExtEnabled ScopedTypeVariables
+  kindSignaturesEnabled <- isExtEnabled KindSignatures
+  when (not scopedTypeVariablesEnabled) $ error [i|The ScopedTypeVariables extension is required; please enable it before calling deriveTypeScript. (For example: put {-# LANGUAGE ScopedTypeVariables #-} at the top of the file.)|]
+  when ((not kindSignaturesEnabled) && (length datatypeVars > 0)) $ error [i|The KindSignatures extension is required since type #{datatypeName} is a higher order type; please enable it before calling deriveTypeScript. (For example: put {-# LANGUAGE KindSignatures #-} at the top of the file.)|]
+#else
+assertExtensionsTurnedOn _ = return ()
 #endif
 
 -- Older versions of Aeson don't have an Eq instance for SumEncoding so we do this
diff --git a/test/Util.hs b/test/Util.hs
--- a/test/Util.hs
+++ b/test/Util.hs
@@ -19,6 +19,7 @@
 import System.IO.Temp
 import System.Process
 
+npmInstallScript = "test/assets/npm_install.sh"
 yarnInstallScript = "test/assets/yarn_install.sh"
 localTSC = "test/assets/node_modules/.bin/tsc"
 
@@ -83,8 +84,11 @@
 ensureTSCExists :: IO ()
 ensureTSCExists = doesFileExist localTSC >>= \exists -> when (not exists) $ void $ do
   cwd <- getCurrentDirectory
+
+  installScript <- chooseInstallScript
+
   putStrLn [i|Invoking yarn to install tsc compiler (make sure yarn is installed). CWD is #{cwd}|]
-  (exitCode, stdout, stderr) <- readProcessWithExitCode yarnInstallScript [] ""
+  (exitCode, stdout, stderr) <- readProcessWithExitCode installScript [] ""
   when (exitCode /= ExitSuccess) $ putStrLn [i|Error installing yarn: '#{stderr}', '#{stdout}'|]
 
 
@@ -95,3 +99,14 @@
 #else
 setTagSingleConstructors = id
 #endif
+
+chooseInstallScript :: IO String
+chooseInstallScript = do
+  yarn <- findExecutable "yarn"
+  case yarn of
+    Just _ -> return yarnInstallScript
+    Nothing -> do
+      npm <- findExecutable "npm"
+      case npm of
+        Just _ -> return npmInstallScript
+        Nothing -> error [i|Couldn't find either yarn or npm; one of them is needed to install a TypeScript compiler.|]
diff --git a/test/assets/npm_install.sh b/test/assets/npm_install.sh
new file mode 100644
--- /dev/null
+++ b/test/assets/npm_install.sh
@@ -0,0 +1,11 @@
+#!/bin/bash
+
+# This helper script will run "npm install" in the directory it's in
+# Useful because older versions of System.Process don't have nice things like readCreateProcess
+
+SCRIPTDIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+
+set -e
+
+cd $SCRIPTDIR
+npm install