diff --git a/src/cmd/link/internal/amd64/asm.go b/src/cmd/link/internal/amd64/asm.go
index 9a3af983a3..7754cf9bfa 100644
--- a/src/cmd/link/internal/amd64/asm.go
+++ b/src/cmd/link/internal/amd64/asm.go
@@ -185,6 +185,38 @@ func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loade
 		}
 		return true
 
+	case objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_SUBTRACTOR*2 + 0:
+		// X86_64_RELOC_SUBTRACTOR must be followed by X86_64_RELOC_UNSIGNED.
+		// The pair of relocations resolves to the difference between two
+		// symbol addresses (each relocation specifies a symbol).
+		// See Darwin's header file include/mach-o/x86_64/reloc.h.
+		// ".quad _foo - _bar" is expressed as
+		// r_type=X86_64_RELOC_SUBTRACTOR, r_length=3, r_extern=1, r_pcrel=0, r_symbolnum=_bar
+		// r_type=X86_64_RELOC_UNSIGNED, r_length=3, r_extern=1, r_pcrel=0, r_symbolnum=_foo
+		//
+		// For the cases we care (the race syso), the symbol being subtracted
+		// out is always in the current section, so we can just convert it to
+		// a PC-relative relocation, with the addend adjusted.
+		// If later we need the more general form, we can introduce objabi.R_DIFF
+		// that works like this Mach-O relocation.
+		su := ldr.MakeSymbolUpdater(s)
+		outer, off := ld.FoldSubSymbolOffset(ldr, targ)
+		if outer != s {
+			ldr.Errorf(s, "unsupported X86_64_RELOC_SUBTRACTOR reloc: target %s, outer %s",
+				ldr.SymName(targ), ldr.SymName(outer))
+			break
+		}
+		relocs := su.Relocs()
+		if rIdx+1 >= relocs.Count() || relocs.At(rIdx+1).Type() != objabi.MachoRelocOffset+ld.MACHO_X86_64_RELOC_UNSIGNED*2+0 || relocs.At(rIdx+1).Off() != r.Off() {
+			ldr.Errorf(s, "unexpected X86_64_RELOC_SUBTRACTOR reloc, must be followed by X86_64_RELOC_UNSIGNED at the same offset: %d %v %d", rIdx, relocs.At(rIdx+1).Type(), relocs.At(rIdx+1).Off())
+		}
+		// The second relocation has the target symbol we want
+		su.SetRelocType(rIdx+1, objabi.R_PCREL)
+		su.SetRelocAdd(rIdx+1, r.Add()+int64(r.Off())-off)
+		// Remove the other relocation
+		su.SetRelocSiz(rIdx, 0)
+		return true
+
 	case objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_BRANCH*2 + 1:
 		if targType == sym.SDYNIMPORT {
 			addpltsym(target, ldr, syms, targ)
diff --git a/src/cmd/link/internal/loader/symbolbuilder.go b/src/cmd/link/internal/loader/symbolbuilder.go
index 8abbb931e5..35749f9ea9 100644
--- a/src/cmd/link/internal/loader/symbolbuilder.go
+++ b/src/cmd/link/internal/loader/symbolbuilder.go
@@ -139,6 +139,11 @@ func (sb *SymbolBuilder) SetRelocAdd(i int, a int64) {
 	sb.relocs[i].SetAdd(a)
 }
 
+// SetRelocAdd sets the size of the 'i'-th relocation on this sym to 'sz'
+func (sb *SymbolBuilder) SetRelocSiz(i int, sz uint8) {
+	sb.relocs[i].SetSiz(sz)
+}
+
 // Add n relocations, return a handle to the relocations.
 func (sb *SymbolBuilder) AddRelocs(n int) Relocs {
 	sb.relocs = append(sb.relocs, make([]goobj.Reloc, n)...)
diff --git a/src/cmd/link/internal/loadmacho/ldmacho.go b/src/cmd/link/internal/loadmacho/ldmacho.go
index 0d2bca28e9..5e8022ce69 100644
--- a/src/cmd/link/internal/loadmacho/ldmacho.go
+++ b/src/cmd/link/internal/loadmacho/ldmacho.go
@@ -790,8 +790,6 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, f *bio.Reader,
 
 			rAdd = 0 // clear rAdd for next iteration
 		}
-
-		sb.SortRelocs()
 	}
 
 	return textp, nil