diff --git a/compiler/rustc_middle/src/mir/mono.rs b/compiler/rustc_middle/src/mir/mono.rs
index c354cdd985b3..776cf002c170 100644
--- a/compiler/rustc_middle/src/mir/mono.rs
+++ b/compiler/rustc_middle/src/mir/mono.rs
@@ -494,14 +494,19 @@ impl CodegenUnitNameBuilder<'tcx> {
                 format!(
                     "-in-{}.{:08x}",
                     tcx.crate_name(LOCAL_CRATE),
-                    local_stable_crate_id.to_u64()
+                    local_stable_crate_id.to_u64() as u32,
                 )
             } else {
                 String::new()
             };
 
             let stable_crate_id = tcx.sess.local_stable_crate_id();
-            format!("{}.{:08x}{}", tcx.crate_name(cnum), stable_crate_id.to_u64(), local_crate_id)
+            format!(
+                "{}.{:08x}{}",
+                tcx.crate_name(cnum),
+                stable_crate_id.to_u64() as u32,
+                local_crate_id,
+            )
         });
 
         write!(cgu_name, "{}", crate_prefix).unwrap();
diff --git a/src/test/ui/lto-duplicate-symbols.stderr b/src/test/ui/lto-duplicate-symbols.stderr
index 891cda8016c3..e4de04ef3ccd 100644
--- a/src/test/ui/lto-duplicate-symbols.stderr
+++ b/src/test/ui/lto-duplicate-symbols.stderr
@@ -1,6 +1,6 @@
 warning: Linking globals named 'foo': symbol multiply defined!
 
-error: failed to load bc of "lto-duplicate-symbols2.lto_duplicate_symbols2.288b404e693a75b4-cgu.0.rcgu.o": 
+error: failed to load bc of "lto-duplicate-symbols2.lto_duplicate_symbols2.693a75b4-cgu.0.rcgu.o": 
 
 error: aborting due to previous error; 1 warning emitted