diff --git a/lld/MachO/ICF.cpp b/lld/MachO/ICF.cpp
--- a/lld/MachO/ICF.cpp
+++ b/lld/MachO/ICF.cpp
@@ -275,7 +275,7 @@
   // Into each origin-section hash, combine all reloc referent section hashes.
   for (icfPass = 0; icfPass < 2; ++icfPass) {
     parallelForEach(icfInputs, [&](ConcatInputSection *isec) {
-      uint64_t hash = isec->icfEqClass[icfPass % 2];
+      uint32_t hash = isec->icfEqClass[icfPass % 2];
       for (const Reloc &r : isec->relocs) {
         if (auto *sym = r.referent.dyn_cast<Symbol *>()) {
           if (auto *defined = dyn_cast<Defined>(sym)) {
@@ -295,7 +295,7 @@
         }
       }
       // Set MSB to 1 to avoid collisions with non-hashed classes.
-      isec->icfEqClass[(icfPass + 1) % 2] = hash | (1ull << 63);
+      isec->icfEqClass[(icfPass + 1) % 2] = hash | (1ull << 31);
     });
   }
 
@@ -391,7 +391,7 @@
     assert(isec->icfEqClass[0] == 0); // don't overwrite a unique ID!
     // Turn-on the top bit to guarantee that valid hashes have no collisions
     // with the small-integer unique IDs for ICF-ineligible sections
-    isec->icfEqClass[0] = xxHash64(isec->data) | (1ull << 63);
+    isec->icfEqClass[0] = xxHash64(isec->data) | (1ull << 31);
   });
   // Now that every input section is either hashed or marked as unique, run the
   // segregation algorithm to detect foldable subsections.
diff --git a/lld/MachO/InputSection.h b/lld/MachO/InputSection.h
--- a/lld/MachO/InputSection.h
+++ b/lld/MachO/InputSection.h
@@ -117,7 +117,7 @@
   // Points to the surviving section after this one is folded by ICF
   ConcatInputSection *replacement = nullptr;
   // Equivalence-class ID for ICF
-  uint64_t icfEqClass[2] = {0, 0};
+  uint32_t icfEqClass[2] = {0, 0};
 
   // With subsections_via_symbols, most symbols have their own InputSection,
   // and for weak symbols (e.g. from inline functions), only the
diff --git a/lld/MachO/InputSection.cpp b/lld/MachO/InputSection.cpp
--- a/lld/MachO/InputSection.cpp
+++ b/lld/MachO/InputSection.cpp
@@ -30,7 +30,7 @@
 // can differ based on STL debug levels (e.g. iterator debugging on MSVC's STL),
 // so account for that.
 static_assert(sizeof(void *) != 8 ||
-                  sizeof(ConcatInputSection) == sizeof(std::vector<Reloc>) + 96,
+                  sizeof(ConcatInputSection) == sizeof(std::vector<Reloc>) + 88,
               "Try to minimize ConcatInputSection's size, we create many "
               "instances of it");