diff --git a/src/rcore/modes.rs b/src/rcore/modes.rs
index 0286d49..036b836 100644
--- a/src/rcore/modes.rs
+++ b/src/rcore/modes.rs
@@ -5,6 +5,8 @@ use super::*;
 pub trait Mode {
     type ParseResult<A, E, I>;
 
+    type ExtensionResult<A, E>;
+
     fn map_err<A, E0, E1, I>(
         result: Self::ParseResult<A, E0, I>,
         f: impl FnOnce(E0) -> E1,
@@ -68,6 +70,8 @@ pub struct RegularMode;
 impl Mode for RegularMode {
     type ParseResult<A, E, I> = Result<A, E>;
 
+    type ExtensionResult<A, E> = Result<A, E>;
+
     fn map_err<A, E0, E1, I>(
         result: Self::ParseResult<A, E0, I>,
         f: impl FnOnce(E0) -> E1,
diff --git a/src/rstd/inlining/modes.rs b/src/rstd/inlining/modes.rs
index 10f3d95..c6dbbcb 100644
--- a/src/rstd/inlining/modes.rs
+++ b/src/rstd/inlining/modes.rs
@@ -5,6 +5,8 @@ pub struct InliningMode;
 impl Mode for InliningMode {
     type ParseResult<A, E, I> = Result<(A, I), E>;
 
+    type ExtensionResult<A, E> = E;
+
     fn map_err<A, E0, E1, I>(
         result: Self::ParseResult<A, E0, I>,
         f: impl FnOnce(E0) -> E1,