diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index c7d0f594f0117..89bb5797a828f 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -1632,7 +1632,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         self.def_path_hash_map.def_path_hash_to_def_index(&hash)
     }
 
-    fn expn_hash_to_expn_id(&self, index_guess: u32, hash: ExpnHash) -> ExpnId {
+    fn expn_hash_to_expn_id(&self, sess: &Session, index_guess: u32, hash: ExpnHash) -> ExpnId {
         debug_assert_eq!(ExpnId::from_hash(hash), None);
         let index_guess = ExpnIndex::from_u32(index_guess);
         let old_hash = self.root.expn_hashes.get(self, index_guess).map(|lazy| lazy.decode(self));
@@ -1654,8 +1654,6 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                     let i = ExpnIndex::from_u32(i);
                     if let Some(hash) = self.root.expn_hashes.get(self, i) {
                         map.insert(hash.decode(self), i);
-                    } else {
-                        panic!("Missing expn_hash entry for {:?}", i);
                     }
                 }
                 map
@@ -1663,7 +1661,7 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
             map[&hash]
         };
 
-        let data = self.root.expn_data.get(self, index).unwrap().decode(self);
+        let data = self.root.expn_data.get(self, index).unwrap().decode((self, sess));
         rustc_span::hygiene::register_expn_id(self.cnum, index, data, hash)
     }
 
diff --git a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
index 292ef03d856d9..4e7f85d2c3727 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
@@ -506,7 +506,13 @@ impl CrateStore for CStore {
         DefId { krate: cnum, index: def_index }
     }
 
-    fn expn_hash_to_expn_id(&self, cnum: CrateNum, index_guess: u32, hash: ExpnHash) -> ExpnId {
-        self.get_crate_data(cnum).expn_hash_to_expn_id(index_guess, hash)
+    fn expn_hash_to_expn_id(
+        &self,
+        sess: &Session,
+        cnum: CrateNum,
+        index_guess: u32,
+        hash: ExpnHash,
+    ) -> ExpnId {
+        self.get_crate_data(cnum).expn_hash_to_expn_id(sess, index_guess, hash)
     }
 }
diff --git a/compiler/rustc_query_impl/src/on_disk_cache.rs b/compiler/rustc_query_impl/src/on_disk_cache.rs
index d8cff0bd1880f..48eb488792d89 100644
--- a/compiler/rustc_query_impl/src/on_disk_cache.rs
+++ b/compiler/rustc_query_impl/src/on_disk_cache.rs
@@ -664,22 +664,32 @@ impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for ExpnId {
 
             let data: ExpnData = decoder
                 .with_position(pos.to_usize(), |decoder| decode_tagged(decoder, TAG_EXPN_DATA))?;
-            rustc_span::hygiene::register_local_expn_id(data, hash)
+            let expn_id = rustc_span::hygiene::register_local_expn_id(data, hash);
+
+            #[cfg(debug_assertions)]
+            {
+                use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+                let mut hcx = decoder.tcx.create_stable_hashing_context();
+                let mut hasher = StableHasher::new();
+                hcx.while_hashing_spans(true, |hcx| {
+                    expn_id.expn_data().hash_stable(hcx, &mut hasher)
+                });
+                let local_hash: u64 = hasher.finish();
+                debug_assert_eq!(hash.local_hash(), local_hash);
+            }
+
+            expn_id
         } else {
             let index_guess = decoder.foreign_expn_data[&hash];
-            decoder.tcx.cstore_untracked().expn_hash_to_expn_id(krate, index_guess, hash)
+            decoder.tcx.cstore_untracked().expn_hash_to_expn_id(
+                decoder.tcx.sess,
+                krate,
+                index_guess,
+                hash,
+            )
         };
 
-        #[cfg(debug_assertions)]
-        {
-            use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
-            let mut hcx = decoder.tcx.create_stable_hashing_context();
-            let mut hasher = StableHasher::new();
-            hcx.while_hashing_spans(true, |hcx| expn_id.expn_data().hash_stable(hcx, &mut hasher));
-            let local_hash: u64 = hasher.finish();
-            debug_assert_eq!(hash.local_hash(), local_hash);
-        }
-
+        debug_assert_eq!(expn_id.krate, krate);
         Ok(expn_id)
     }
 }
diff --git a/compiler/rustc_session/src/cstore.rs b/compiler/rustc_session/src/cstore.rs
index 9d6bd20103989..59e7abc2ea3bd 100644
--- a/compiler/rustc_session/src/cstore.rs
+++ b/compiler/rustc_session/src/cstore.rs
@@ -4,6 +4,7 @@
 
 use crate::search_paths::PathKind;
 use crate::utils::NativeLibKind;
+use crate::Session;
 use rustc_ast as ast;
 use rustc_data_structures::sync::{self, MetadataRef};
 use rustc_hir::def_id::{CrateNum, DefId, StableCrateId, LOCAL_CRATE};
@@ -193,7 +194,13 @@ pub trait CrateStore: std::fmt::Debug {
 
     /// Fetch a DefId from a DefPathHash for a foreign crate.
     fn def_path_hash_to_def_id(&self, cnum: CrateNum, hash: DefPathHash) -> DefId;
-    fn expn_hash_to_expn_id(&self, cnum: CrateNum, index_guess: u32, hash: ExpnHash) -> ExpnId;
+    fn expn_hash_to_expn_id(
+        &self,
+        sess: &Session,
+        cnum: CrateNum,
+        index_guess: u32,
+        hash: ExpnHash,
+    ) -> ExpnId;
 }
 
 pub type CrateStoreDyn = dyn CrateStore + sync::Sync;
diff --git a/src/test/incremental/mir-opt.rs b/src/test/incremental/mir-opt.rs
new file mode 100644
index 0000000000000..5bd863439df5d
--- /dev/null
+++ b/src/test/incremental/mir-opt.rs
@@ -0,0 +1,11 @@
+// MIR optimizations can create expansions after the TyCtxt has been created.
+// This test verifies that those expansions can be decoded correctly.
+
+// revisions:rpass1 rpass2
+// compile-flags: -Z query-dep-graph -Z mir-opt-level=3
+
+fn main() {
+    if std::env::var("a").is_ok() {
+        println!("b");
+    }
+}