diff --git a/compiler/rustc_index/Cargo.toml b/compiler/rustc_index/Cargo.toml
index e46a1a7f7606f..edcd7816a60e0 100644
--- a/compiler/rustc_index/Cargo.toml
+++ b/compiler/rustc_index/Cargo.toml
@@ -8,7 +8,7 @@ edition = "2024"
 rustc_index_macros = { path = "../rustc_index_macros" }
 rustc_macros = { path = "../rustc_macros", optional = true }
 rustc_serialize = { path = "../rustc_serialize", optional = true }
-smallvec = "1.8.1"
+smallvec = { version = "1.8.1", optional = true }
 # tidy-alphabetical-end
 
 [features]
@@ -17,6 +17,7 @@ default = ["nightly"]
 nightly = [
     "dep:rustc_macros",
     "dep:rustc_serialize",
+    "dep:smallvec",
     "rustc_index_macros/nightly",
 ]
 rustc_randomized_layouts = []
diff --git a/compiler/rustc_type_ir_macros/Cargo.toml b/compiler/rustc_type_ir_macros/Cargo.toml
index 15a5557509929..14bffa403a867 100644
--- a/compiler/rustc_type_ir_macros/Cargo.toml
+++ b/compiler/rustc_type_ir_macros/Cargo.toml
@@ -10,6 +10,6 @@ proc-macro = true
 # tidy-alphabetical-start
 proc-macro2 = "1"
 quote = "1"
-syn = { version = "2.0.9", features = ["full"] }
+syn = { version = "2.0.9", features = ["full", "visit-mut"] }
 synstructure = "0.13.0"
 # tidy-alphabetical-end