diff --git a/src/common/reason.ml b/src/common/reason.ml
index 1a892b478b8..cd0b9edc399 100644
--- a/src/common/reason.ml
+++ b/src/common/reason.ml
@@ -164,7 +164,6 @@ type 'loc virtual_reason_desc =
   | RRestParameter of string option
   | RPatternParameter of string
   | RIdentifier of name
-  | RUnknownParameter of string
   | RIdentifierAssignment of string
   | RPropertyAssignment of string option
   | RProperty of name option
@@ -295,13 +294,13 @@ let rec map_desc_locs f = function
     | RDefaultValue | RConstructor | RReturn | RDefaultConstructor | RRegExp | RSuper | RNoSuper
     | RDummyPrototype | RDummyThis | RTupleMap | RObjectMap | RType _ | RTypeof _ | RMethod _
     | RMethodCall _ | RParameter _ | RRestParameter _ | RPatternParameter _ | RIdentifier _
-    | RUnknownParameter _ | RIdentifierAssignment _ | RPropertyAssignment _ | RProperty _
-    | RPrivateProperty _ | RMember _ | RPropertyIsAString _ | RMissingProperty _
-    | RUnknownProperty _ | RUndefinedProperty _ | RSomeProperty | RFieldInitializer _
-    | RUntypedModule _ | RNamedImportedType _ | RImportStarType _ | RImportStarTypeOf _
-    | RImportStar _ | RDefaultImportedType _ | RAsyncImport | RCode _ | RCustom _
-    | RIncompatibleInstantiation _ | ROpaqueType _ | RObjectMapi | RObjectKeyMirror
-    | RObjectMapConst | RIndexedAccess _ | RConditionalType | RInferType _ ) as r ->
+    | RIdentifierAssignment _ | RPropertyAssignment _ | RProperty _ | RPrivateProperty _ | RMember _
+    | RPropertyIsAString _ | RMissingProperty _ | RUnknownProperty _ | RUndefinedProperty _
+    | RSomeProperty | RFieldInitializer _ | RUntypedModule _ | RNamedImportedType _
+    | RImportStarType _ | RImportStarTypeOf _ | RImportStar _ | RDefaultImportedType _
+    | RAsyncImport | RCode _ | RCustom _ | RIncompatibleInstantiation _ | ROpaqueType _
+    | RObjectMapi | RObjectKeyMirror | RObjectMapConst | RIndexedAccess _ | RConditionalType
+    | RInferType _ ) as r ->
     r
   | RConstructorCall desc -> RConstructorCall (map_desc_locs f desc)
   | RTypeAlias (s, None, d) -> RTypeAlias (s, None, map_desc_locs f d)
@@ -665,7 +664,6 @@ let rec string_of_desc = function
   | RMethod (Some x) -> spf "method `%s`" x
   | RMethod None -> "computed method"
   | RIdentifier x -> spf "`%s`" (prettify_react_util (display_string_of_name x))
-  | RUnknownParameter x -> spf "parameter `%s` of unknown type" (prettify_react_util x)
   | RIdentifierAssignment x -> spf "assignment of identifier `%s`" x
   | RMethodCall (Some x) -> spf "call of method `%s`" x
   | RMethodCall None -> "call of computed property"
@@ -1492,7 +1490,6 @@ let classification_of_reason r =
   | RRestParameter _
   | RPatternParameter _
   | RIdentifier _
-  | RUnknownParameter _
   | RIdentifierAssignment _
   | RPropertyAssignment _
   | RProperty _
diff --git a/src/common/reason.mli b/src/common/reason.mli
index 6d8f6e15571..36aebe8c244 100644
--- a/src/common/reason.mli
+++ b/src/common/reason.mli
@@ -123,7 +123,6 @@ type 'loc virtual_reason_desc =
   | RRestParameter of string option
   | RPatternParameter of string
   | RIdentifier of name
-  | RUnknownParameter of string
   | RIdentifierAssignment of string
   | RPropertyAssignment of string option
   | RProperty of name option
diff --git a/src/typing/errors/flow_error.ml b/src/typing/errors/flow_error.ml
index b8df76f1b72..c30694448fb 100644
--- a/src/typing/errors/flow_error.ml
+++ b/src/typing/errors/flow_error.ml
@@ -1190,30 +1190,6 @@ let rec make_error_printable :
               code (string_of_int n);
               text " characters are not treated as literals";
             ]
-        | (RUnknownParameter n, _) ->
-          let message =
-            [
-              ref lower;
-              text " is incompatible with ";
-              ref upper;
-              text " (consider adding a type annotation to ";
-              ref (update_desc_reason (fun _ -> RIdentifier (OrdinaryName n)) lower);
-              text ")";
-            ]
-          in
-          make_error lower message
-        | (_, RUnknownParameter n) ->
-          let message =
-            [
-              ref lower;
-              text " is incompatible with ";
-              ref upper;
-              text " (consider adding a type annotation to ";
-              ref (update_desc_reason (fun _ -> RIdentifier (OrdinaryName n)) upper);
-              text ")";
-            ]
-          in
-          make_error lower message
         | _ -> make_error lower [ref lower; text " is incompatible with "; ref upper]
       end)
   in