diff --git a/src/librustc/ty/context.rs b/src/librustc/ty/context.rs
index 82095a2f5b01d..f78fad9f7aa9a 100644
--- a/src/librustc/ty/context.rs
+++ b/src/librustc/ty/context.rs
@@ -823,12 +823,6 @@ impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for TypeckTables<'gcx> {
 
 impl<'tcx> CommonTypes<'tcx> {
     fn new(interners: &CtxtInterners<'tcx>) -> CommonTypes<'tcx> {
-        // Ensure our type representation does not grow
-        #[cfg(target_pointer_width = "64")]
-        static_assert!(ASSERT_TY_KIND: ::std::mem::size_of::<ty::TyKind<'_>>() <= 24);
-        #[cfg(target_pointer_width = "64")]
-        static_assert!(ASSERT_TYS: ::std::mem::size_of::<ty::TyS<'_>>() <= 32);
-
         let mk = |sty| CtxtInterners::intern_ty(interners, interners, sty);
         let mk_region = |r| {
             if let Some(r) = interners.region.borrow().get(&r) {
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index ef9b3e3efab27..3250342613510 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -514,6 +514,10 @@ pub struct TyS<'tcx> {
     outer_exclusive_binder: ty::DebruijnIndex,
 }
 
+// `TyS` is used a lot. Make sure it doesn't unintentionally get bigger.
+#[cfg(target_arch = "x86_64")]
+static_assert!(MEM_SIZE_OF_TY_S: ::std::mem::size_of::<TyS<'_>>() == 32);
+
 impl<'tcx> Ord for TyS<'tcx> {
     fn cmp(&self, other: &TyS<'tcx>) -> Ordering {
         self.sty.cmp(&other.sty)
diff --git a/src/librustc/ty/sty.rs b/src/librustc/ty/sty.rs
index a4130bf15cb82..bd3a34cae90f4 100644
--- a/src/librustc/ty/sty.rs
+++ b/src/librustc/ty/sty.rs
@@ -211,6 +211,10 @@ pub enum TyKind<'tcx> {
     Error,
 }
 
+// `TyKind` is used a lot. Make sure it doesn't unintentionally get bigger.
+#[cfg(target_arch = "x86_64")]
+static_assert!(MEM_SIZE_OF_TY_KIND: ::std::mem::size_of::<TyKind<'_>>() == 24);
+
 /// A closure can be modeled as a struct that looks like:
 ///
 ///     struct Closure<'l0...'li, T0...Tj, CK, CS, U0...Uk> {
diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index fa6fe34783389..808e19d6f120f 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -20,6 +20,7 @@ use print::pprust;
 use ptr::P;
 use rustc_data_structures::indexed_vec;
 use rustc_data_structures::indexed_vec::Idx;
+#[cfg(target_arch = "x86_64")]
 use rustc_data_structures::static_assert;
 use rustc_target::spec::abi::Abi;
 use source_map::{dummy_spanned, respan, Spanned};