diff --git a/compiler/rustc_data_structures/src/profiling.rs b/compiler/rustc_data_structures/src/profiling.rs
index 572bd4ac21c32..5e13e7c8aafc8 100644
--- a/compiler/rustc_data_structures/src/profiling.rs
+++ b/compiler/rustc_data_structures/src/profiling.rs
@@ -101,7 +101,7 @@ use parking_lot::RwLock;
 use smallvec::SmallVec;
 
 bitflags::bitflags! {
-    struct EventFilter: u32 {
+    struct EventFilter: u16 {
         const GENERIC_ACTIVITIES  = 1 << 0;
         const QUERY_PROVIDERS     = 1 << 1;
         const QUERY_CACHE_HITS    = 1 << 2;
diff --git a/compiler/rustc_middle/src/ty/adt.rs b/compiler/rustc_middle/src/ty/adt.rs
index 6187fc43cf88b..ad9891a5dca68 100644
--- a/compiler/rustc_middle/src/ty/adt.rs
+++ b/compiler/rustc_middle/src/ty/adt.rs
@@ -26,7 +26,7 @@ use super::{Destructor, FieldDef, GenericPredicates, Ty, TyCtxt, VariantDef, Var
 
 bitflags! {
     #[derive(HashStable, TyEncodable, TyDecodable)]
-    pub struct AdtFlags: u32 {
+    pub struct AdtFlags: u16 {
         const NO_ADT_FLAGS        = 0;
         /// Indicates whether the ADT is an enum.
         const IS_ENUM             = 1 << 0;
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 23d6242899f2e..88b084bbccbdc 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -1739,7 +1739,7 @@ pub struct Destructor {
 
 bitflags! {
     #[derive(HashStable, TyEncodable, TyDecodable)]
-    pub struct VariantFlags: u32 {
+    pub struct VariantFlags: u8 {
         const NO_VARIANT_FLAGS        = 0;
         /// Indicates whether the field list of this variant is `#[non_exhaustive]`.
         const IS_FIELD_LIST_NON_EXHAUSTIVE = 1 << 0;
diff --git a/compiler/rustc_target/src/abi/call/mod.rs b/compiler/rustc_target/src/abi/call/mod.rs
index 57011aa8a1474..52159a7b06aa5 100644
--- a/compiler/rustc_target/src/abi/call/mod.rs
+++ b/compiler/rustc_target/src/abi/call/mod.rs
@@ -65,7 +65,7 @@ mod attr_impl {
     // The subset of llvm::Attribute needed for arguments, packed into a bitfield.
     bitflags::bitflags! {
         #[derive(Default, HashStable_Generic)]
-        pub struct ArgAttribute: u16 {
+        pub struct ArgAttribute: u8 {
             const NoAlias   = 1 << 1;
             const NoCapture = 1 << 2;
             const NonNull   = 1 << 3;