diff --git a/src/julia_internal.h b/src/julia_internal.h
index 04effee838a4b..368331f0da74d 100644
--- a/src/julia_internal.h
+++ b/src/julia_internal.h
@@ -61,9 +61,12 @@ void *jl_gc_perm_alloc(size_t sz);
 static const int jl_gc_sizeclasses[JL_GC_N_POOLS] = {
 #ifdef _P64
     8,
-#elif defined(_CPU_ARM_) || defined(_CPU_PPC_)
+#elif defined(_CPU_ARM_) || defined(_CPU_PPC_) || defined(_CPU_X86_)
     // ARM and PowerPC have max alignment of 8,
     // make sure allocation of size 8 has that alignment.
+    // for x86 alignment is important for atomic ops and
+    // the corresponding platform ABI. Once we can use
+    // libatomic on Windows this is no longer necessary.
     4, 8,
 #else
     4, 8, 12,
@@ -99,7 +102,7 @@ STATIC_INLINE int jl_gc_alignment(size_t sz)
 #ifdef _P64
     (void)sz;
     return 16;
-#elif defined(_CPU_ARM_) || defined(_CPU_PPC_)
+#elif defined(_CPU_ARM_) || defined(_CPU_PPC_) || defined(_CPU_X86_)
     return sz <= 4 ? 8 : 16;
 #else
     // szclass 8
@@ -120,7 +123,7 @@ STATIC_INLINE int JL_CONST_FUNC jl_gc_szclass(size_t sz)
     if (sz <=    8)
         return 0;
     const int N = 0;
-#elif defined(_CPU_ARM_) || defined(_CPU_PPC_)
+#elif defined(_CPU_ARM_) || defined(_CPU_PPC_) || defined(_CPU_X86_)
     if (sz <=    8)
         return (sz + 3) / 4 - 1;
     const int N = 1;
diff --git a/src/julia_threads.h b/src/julia_threads.h
index 5e80e3d1a77e4..1b5eb5ad11856 100644
--- a/src/julia_threads.h
+++ b/src/julia_threads.h
@@ -56,7 +56,7 @@ typedef struct {
     // variables for allocating objects from pools
 #ifdef _P64
 #  define JL_GC_N_POOLS 41
-#elif defined(_CPU_ARM_) || defined(_CPU_PPC_)
+#elif defined(_CPU_ARM_) || defined(_CPU_PPC_) || defined(_CPU_X86_)
 #  define JL_GC_N_POOLS 42
 #else
 #  define JL_GC_N_POOLS 43