diff --git a/lld/MachO/Writer.cpp b/lld/MachO/Writer.cpp
--- a/lld/MachO/Writer.cpp
+++ b/lld/MachO/Writer.cpp
@@ -20,6 +20,7 @@
 #include "SyntheticSections.h"
 #include "Target.h"
 #include "UnwindInfoSection.h"
+#include "llvm/Support/Parallel.h"
 
 #include "lld/Common/Arrays.h"
 #include "lld/Common/CommonLinkerContext.h"
@@ -1081,9 +1082,13 @@
 
 void Writer::writeSections() {
   uint8_t *buf = buffer->getBufferStart();
+  std::vector<const OutputSection *> osecs;
   for (const OutputSegment *seg : outputSegments)
-    for (const OutputSection *osec : seg->getSections())
-      osec->writeTo(buf + osec->fileOff);
+    append_range(osecs, seg->getSections());
+
+  parallelForEach(osecs.begin(), osecs.end(), [&](const OutputSection *osec) {
+    osec->writeTo(buf + osec->fileOff);
+  });
 }
 
 // In order to utilize multiple cores, we first split the buffer into chunks,
diff --git a/lld/test/MachO/invalid/range-check.s b/lld/test/MachO/invalid/range-check.s
--- a/lld/test/MachO/invalid/range-check.s
+++ b/lld/test/MachO/invalid/range-check.s
@@ -6,11 +6,11 @@
 # RUN: %lld -dylib %t/bar.o -o %t/libbar.dylib
 # RUN: not %lld -lSystem -o /dev/null %t/libbar.dylib %t/test.o 2>&1 | FileCheck %s
 
-# CHECK: error: {{.*}}test.o:(symbol _main+0xd): relocation UNSIGNED is out of range: [[#]] is not in [0, 4294967295]; references _foo
-# CHECK: error: {{.*}}test.o:(symbol _main+0x3): relocation GOT_LOAD is out of range: [[#]] is not in [-2147483648, 2147483647]; references _foo
-# CHECK: error: stub is out of range: [[#]] is not in [-2147483648, 2147483647]; references _bar
-# CHECK: error: stub helper header is out of range: [[#]] is not in [-2147483648, 2147483647]
-# CHECK: error: stub helper header is out of range: [[#]] is not in [-2147483648, 2147483647]
+# CHECK-DAG: error: {{.*}}test.o:(symbol _main+0xd): relocation UNSIGNED is out of range: [[#]] is not in [0, 4294967295]; references _foo
+# CHECK-DAG: error: {{.*}}test.o:(symbol _main+0x3): relocation GOT_LOAD is out of range: [[#]] is not in [-2147483648, 2147483647]; references _foo
+# CHECK-DAG: error: stub is out of range: [[#]] is not in [-2147483648, 2147483647]; references _bar
+# CHECK-DAG: error: stub helper header is out of range: [[#]] is not in [-2147483648, 2147483647]
+# CHECK-DAG: error: stub helper header is out of range: [[#]] is not in [-2147483648, 2147483647]
 
 #--- bar.s
 .globl _bar