diff --git a/README.md b/README.md
index 44c043e..3a6a6e9 100644
--- a/README.md
+++ b/README.md
@@ -62,6 +62,7 @@ The decoders we produce require these extra Elm packages installed:
 ``` sh
 elm package install NoRedInk/elm-decode-pipeline
 elm package install krisajenkins/elm-exts
+elm-package install justinmimbs/elm-date-extra
 ```
 
 ## Development
diff --git a/src/Elm/Encoder.hs b/src/Elm/Encoder.hs
index 2b3ceac..f7e4db6 100644
--- a/src/Elm/Encoder.hs
+++ b/src/Elm/Encoder.hs
@@ -127,7 +127,7 @@ instance HasEncoder ElmValue where
   render _ = error "HasEncoderRef ElmValue: should not happen"
 
 instance HasEncoderRef ElmPrimitive where
-  renderRef EDate = pure $ parens "Json.Encode.string << toString"
+  renderRef EDate = pure $ parens "Json.Encode.string << toUtcIsoString"
   renderRef EUnit = pure "Json.Encode.null"
   renderRef EInt = pure "Json.Encode.int"
   renderRef EChar = pure "Json.Encode.char"