diff --git a/lld/lib/ReaderWriter/MachO/MachOLinkingContext.cpp b/lld/lib/ReaderWriter/MachO/MachOLinkingContext.cpp
index 7fb493088338..ad8f8bfa73e2 100644
--- a/lld/lib/ReaderWriter/MachO/MachOLinkingContext.cpp
+++ b/lld/lib/ReaderWriter/MachO/MachOLinkingContext.cpp
@@ -160,6 +160,26 @@ void MachOLinkingContext::configure(HeaderFileType type, Arch arch, OS os,
   _os = os;
   _osMinVersion = minOSVersion;
 
+  // If min OS not specified on command line, use reasonable defaults.
+  if (minOSVersion == 0) {
+    switch (_arch) {
+    case arch_x86_64:
+    case arch_x86:
+      parsePackedVersion("10.8", _osMinVersion);
+      _os = MachOLinkingContext::OS::macOSX;
+      break;
+    case arch_armv6:
+    case arch_armv7:
+    case arch_armv7s:
+    case arch_arm64:
+      parsePackedVersion("7.0", _osMinVersion);
+      _os = MachOLinkingContext::OS::iOS;
+      break;
+    default:
+      break;
+    }
+  }
+
   switch (_outputMachOType) {
   case llvm::MachO::MH_EXECUTE:
     // If targeting newer OS, use _main
diff --git a/lld/test/mach-o/exe-segment-overlap.yaml b/lld/test/mach-o/exe-segment-overlap.yaml
index ec818969de69..1fbc84123182 100644
--- a/lld/test/mach-o/exe-segment-overlap.yaml
+++ b/lld/test/mach-o/exe-segment-overlap.yaml
@@ -1,9 +1,9 @@
-# RUN: lld -flavor darwin -arch x86_64 %s -o %t
+# RUN: lld -flavor darwin -arch x86_64 %s -o %t %p/Inputs/libSystem.yaml
 # RUN: llvm-readobj -sections -section-data %t | FileCheck %s
 
 --- !native
 defined-atoms:
-   - name:            start
+   - name:            _main
      scope:           global
      content:         [ 90 ]
 
@@ -19,26 +19,6 @@ defined-atoms:
      section-name:    __CUST/__custom
 
 
---- !mach-o
-arch:            x86_64
-file-type:       MH_DYLIB
-flags:           [ ]
-install-name:    /usr/lib/libSystem.B.dylib
-sections:
-  - segment:         __TEXT
-    section:         __text
-    type:            S_REGULAR
-    attributes:      [ S_ATTR_PURE_INSTRUCTIONS, S_ATTR_SOME_INSTRUCTIONS ]
-    address:         0x0000000000000000
-    content:         [ 0x55 ]
-
-global-symbols:
-  - name:            dyld_stub_binder
-    type:            N_SECT
-    scope:           [ N_EXT ]
-    sect:            1
-    value:           0x0000000000000000
-
 # CHECK-LABEL: Section {
 # CHECK:     Name: __text
 # CHECK:     Segment: __TEXT
diff --git a/lld/test/mach-o/hello-world-arm64.yaml b/lld/test/mach-o/hello-world-arm64.yaml
index f6b030648754..a0555e9cc426 100644
--- a/lld/test/mach-o/hello-world-arm64.yaml
+++ b/lld/test/mach-o/hello-world-arm64.yaml
@@ -1,4 +1,4 @@
-# RUN: lld -flavor darwin -arch arm64 -ios_version_min 7.0 %s -o %t  && \
+# RUN: lld -flavor darwin -arch arm64 %s -o %t
 # RUN: llvm-nm -m -n %t | FileCheck %s
 #
 # Test that arm64 hello-world can be linked into a mach-o executable
diff --git a/lld/test/mach-o/hello-world-armv6.yaml b/lld/test/mach-o/hello-world-armv6.yaml
index c24d0897795c..746ee094da68 100644
--- a/lld/test/mach-o/hello-world-armv6.yaml
+++ b/lld/test/mach-o/hello-world-armv6.yaml
@@ -1,4 +1,4 @@
-# RUN: lld -flavor darwin -arch armv6 -ios_version_min 7.0 %s -o %t  && \
+# RUN: lld -flavor darwin -arch armv6 %s -o %t
 # RUN: llvm-nm -m %t | FileCheck %s
 #
 # Test that armv6 (arm) hello-world can be linked into a mach-o executable
diff --git a/lld/test/mach-o/hello-world-armv7.yaml b/lld/test/mach-o/hello-world-armv7.yaml
index 54f737bda52e..bfc03c382a05 100644
--- a/lld/test/mach-o/hello-world-armv7.yaml
+++ b/lld/test/mach-o/hello-world-armv7.yaml
@@ -1,4 +1,4 @@
-# RUN: lld -flavor darwin -arch armv7 -ios_version_min 7.0 %s -o %t  && \
+# RUN: lld -flavor darwin -arch armv7 %s -o %t
 # RUN: llvm-nm -m -n %t | FileCheck %s
 #
 # Test that armv7 (thumb) hello-world can be linked into a mach-o executable
diff --git a/lld/test/mach-o/hello-world-x86.yaml b/lld/test/mach-o/hello-world-x86.yaml
index d8f7b52d6ae0..de453ed1ac45 100644
--- a/lld/test/mach-o/hello-world-x86.yaml
+++ b/lld/test/mach-o/hello-world-x86.yaml
@@ -1,4 +1,4 @@
-# RUN: lld -flavor darwin -arch i386 -macosx_version_min 10.8 %s -o %t  && \
+# RUN: lld -flavor darwin -arch i386 %s -o %t
 # RUN: llvm-nm -m %t | FileCheck %s
 #
 # Test that i386 hello-world can be linked into a mach-o executable
diff --git a/lld/test/mach-o/hello-world-x86_64.yaml b/lld/test/mach-o/hello-world-x86_64.yaml
index 985ab5f31cf8..83d4fcb32601 100644
--- a/lld/test/mach-o/hello-world-x86_64.yaml
+++ b/lld/test/mach-o/hello-world-x86_64.yaml
@@ -1,8 +1,8 @@
-# RUN: lld -flavor darwin -arch x86_64 -macosx_version_min 10.8 %s -o %t  && \
+# RUN: lld -flavor darwin -arch x86_64  %s -o %t
 # RUN: llvm-nm -m -n %t | FileCheck %s
 #
-# RUN: lld -flavor darwin -arch x86_64 -macosx_version_min 10.8 %s -dead_strip \
-# RUN:  -o %t2 &&  llvm-nm -m -n %t2 | FileCheck %s
+# RUN: lld -flavor darwin -arch x86_64  %s -dead_strip -o %t2
+# RUN: llvm-nm -m -n %t2 | FileCheck %s
 #
 # Test that x86_64 hello-world can be linked into a mach-o executable
 #