diff --git a/infer/man/man1/infer-full.txt b/infer/man/man1/infer-full.txt
index 6ebc30f56..716490984 100644
--- a/infer/man/man1/infer-full.txt
+++ b/infer/man/man1/infer-full.txt
@@ -1667,11 +1667,12 @@ INTERNAL OPTIONS
            This feature is needed for compatibility reasons. (Conversely:
            --no-nullsafe-disable-field-not-initialized-in-nonstrict-classes)
 
-       --no-nullsafe-optimistic-third-party-params-in-non-strict
-           Deactivates: Nullsafe: in this mode we treat non annotated third
-           party method params as if they were annotated as nullable.
-           (Conversely:
-           --nullsafe-optimistic-third-party-params-in-non-strict)
+       --no-nullsafe-optimistic-third-party-in-default-mode
+           Deactivates: Nullsafe: Unless @Nullsafe annotation is used, treat
+           not annotated third party method params as if they were annotated
+           as nullable, and return values as if they were annotated as
+           non-null (Conversely:
+           --nullsafe-optimistic-third-party-in-default-mode)
 
        --nullsafe-strict-containers
            Activates: Warn when containers are used with nullable keys or
diff --git a/infer/src/base/Config.ml b/infer/src/base/Config.ml
index 2a846c5a4..db7576bef 100644
--- a/infer/src/base/Config.ml
+++ b/infer/src/base/Config.ml
@@ -1650,17 +1650,15 @@ and nullsafe_disable_field_not_initialized_in_nonstrict_classes =
      marked as @NullsafeStrict. This feature is needed for compatibility reasons."
 
 
-and nullsafe_optimistic_third_party_params_in_non_strict =
+and nullsafe_optimistic_third_party_in_default_mode =
   CLOpt.mk_bool
     ~long:
-      "nullsafe-optimistic-third-party-params-in-non-strict"
-      (* Turned on for compatibility reasons.
-         Historically this is because there was no actionable way to change third party annotations.
-         Now that we have such a support, this behavior should be reconsidered, provided
-         our tooling and error reporting is friendly enough to be smoothly used by developers.
-      *) ~default:true
-    "Nullsafe: in this mode we treat non annotated third party method params as if they were \
-     annotated as nullable."
+      "nullsafe-optimistic-third-party-in-default-mode"
+      (* Turned on for compatibility reasons
+       *) ~default:true
+    "Nullsafe: Unless @Nullsafe annotation is used, treat not annotated third party method params \
+     as if they were annotated as nullable, and return values as if they were annotated as \
+     non-null"
 
 
 and nullsafe_third_party_signatures =
@@ -2996,8 +2994,8 @@ and nullsafe_disable_field_not_initialized_in_nonstrict_classes =
   !nullsafe_disable_field_not_initialized_in_nonstrict_classes
 
 
-and nullsafe_optimistic_third_party_params_in_non_strict =
-  !nullsafe_optimistic_third_party_params_in_non_strict
+and nullsafe_optimistic_third_party_in_default_mode =
+  !nullsafe_optimistic_third_party_in_default_mode
 
 
 and nullsafe_third_party_signatures = !nullsafe_third_party_signatures
diff --git a/infer/src/base/Config.mli b/infer/src/base/Config.mli
index e9c4103fe..b61397769 100644
--- a/infer/src/base/Config.mli
+++ b/infer/src/base/Config.mli
@@ -401,7 +401,7 @@ val nullsafe_annotation_graph : bool
 
 val nullsafe_disable_field_not_initialized_in_nonstrict_classes : bool
 
-val nullsafe_optimistic_third_party_params_in_non_strict : bool
+val nullsafe_optimistic_third_party_in_default_mode : bool
 
 val nullsafe_third_party_signatures : string option
 
diff --git a/infer/src/nullsafe/AssignmentRule.ml b/infer/src/nullsafe/AssignmentRule.ml
index f9e507cf3..3011817ee 100644
--- a/infer/src/nullsafe/AssignmentRule.ml
+++ b/infer/src/nullsafe/AssignmentRule.ml
@@ -49,8 +49,9 @@ module ReportableViolation = struct
 
   let from nullsafe_mode ({lhs; rhs} as violation) =
     let falls_under_optimistic_third_party =
-      Config.nullsafe_optimistic_third_party_params_in_non_strict
+      Config.nullsafe_optimistic_third_party_in_default_mode
       && NullsafeMode.equal nullsafe_mode Default
+      (* Treat third party params as if they were [@Nullable] *)
       && Nullability.equal (AnnotatedNullability.get_nullability lhs) ThirdPartyNonnull
     in
     let is_non_reportable =
diff --git a/infer/src/nullsafe/ErrorRenderingUtils.ml b/infer/src/nullsafe/ErrorRenderingUtils.ml
index 42e647856..c70d074e8 100644
--- a/infer/src/nullsafe/ErrorRenderingUtils.ml
+++ b/infer/src/nullsafe/ErrorRenderingUtils.ml
@@ -150,12 +150,8 @@ let mk_recommendation_for_third_party_field nullsafe_mode field =
   match nullsafe_mode with
   | NullsafeMode.Strict ->
       F.sprintf "access %s via a nullsafe strict getter" field
-  | NullsafeMode.Local _ ->
+  | NullsafeMode.Local _ | NullsafeMode.Default ->
       F.sprintf "access %s via a nullsafe getter" field
-  | NullsafeMode.Default ->
-      Logging.die InternalError
-        "mk_recommendation_for_third_party_field:: Should not happen: we should tolerate third \
-         party in default mode"
 
 
 let get_info object_origin nullsafe_mode untrusted_kind =
diff --git a/infer/src/nullsafe/Nullability.ml b/infer/src/nullsafe/Nullability.ml
index a9945f12b..3e9bce55e 100644
--- a/infer/src/nullsafe/Nullability.ml
+++ b/infer/src/nullsafe/Nullability.ml
@@ -68,8 +68,10 @@ let is_considered_nonnull ~nullsafe_mode nullability =
       | NullsafeMode.Local NullsafeMode.Trust.All ->
           UncheckedNonnull
       | NullsafeMode.Default ->
-          (* In default mode, we trust everything, even not annotated third party. *)
-          ThirdPartyNonnull
+          (* We trust all internal method declarations, and, if specified separately,
+             even not annotated third party. *)
+          if Config.nullsafe_optimistic_third_party_in_default_mode then ThirdPartyNonnull
+          else UncheckedNonnull
     in
     is_subtype ~subtype:nullability ~supertype:least_required