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diff --git a/ghc/docs/users_guide/using.vsgml b/ghc/docs/users_guide/using.vsgml
index 23055de..934ef56 100644
--- a/ghc/docs/users_guide/using.vsgml
+++ b/ghc/docs/users_guide/using.vsgml
@@ -397,6 +397,21 @@ mention of it in the export list.
This option is on by default.
+-fwarn-type-defaults:
+-fwarn-type-defaults option
+defaulting mechanism, warning
+
+Have the compiler warn/inform you where in your source the Haskell
+defaulting mechanism for numeric types kicks in. This is useful
+information when converting code from a context that assumed one
+default into one with another, e.g., the 'default default' for Haskell
+1.4 caused the otherwise unconstrained value 1 to be given
+the type Int, whereas Haskell 98 defaults it to
+Integer. This may lead to differences in performance and
+behaviour, hence the usefulness of being non-silent about this.
+
+This warning is off by default.
+
@-fwarn-missing-signatures@:
-fwarn-missing-signatures option
type signatures, missing