diff --git a/llvm/lib/ObjectYAML/MachOEmitter.cpp b/llvm/lib/ObjectYAML/MachOEmitter.cpp
--- a/llvm/lib/ObjectYAML/MachOEmitter.cpp
+++ b/llvm/lib/ObjectYAML/MachOEmitter.cpp
@@ -494,7 +494,8 @@
   writeFatArchs(OS);
 
   auto &FatFile = *ObjectFile.FatMachO;
-  assert(FatFile.FatArchs.size() == FatFile.Slices.size());
+  assert(FatFile.FatArchs.size() > FatFile.Slices.size() &&
+         "Cannot write Slices if not decribed in FatArches");
   for (size_t i = 0; i < FatFile.Slices.size(); i++) {
     ZeroToOffset(OS, FatFile.FatArchs[i].offset);
     MachOWriter Writer(FatFile.Slices[i]);
diff --git a/llvm/test/Object/Inputs/macho-invalid-fat-arch-size b/llvm/test/Object/Inputs/macho-invalid-fat-arch-size
deleted file mode 100644
index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000
GIT binary patch
literal 0
Hc$@<O00001

literal 0
Hc$@<O00001

diff --git a/llvm/test/Object/Inputs/macho-invalid-fat-arch-size.yaml b/llvm/test/Object/Inputs/macho-invalid-fat-arch-size.yaml
new file mode 100644
--- /dev/null
+++ b/llvm/test/Object/Inputs/macho-invalid-fat-arch-size.yaml
@@ -0,0 +1,12 @@
+--- !fat-mach-o
+FatHeader:       
+  magic:           0xCAFEBABE
+  nfat_arch:       1
+FatArchs:        
+  - cputype:         0x00000007
+    cpusubtype:      0x00000003
+    offset:          0x000000000000020
+    size:            32
+    align:           2
+Slices:
+...
diff --git a/llvm/test/Object/macho-invalid.test b/llvm/test/Object/macho-invalid.test
--- a/llvm/test/Object/macho-invalid.test
+++ b/llvm/test/Object/macho-invalid.test
@@ -491,8 +491,8 @@
 RUN: not llvm-objdump --macho --universal-headers %p/Inputs/macho-invalid-fat-header 2>&1 | FileCheck -check-prefix INVALID-FAT-HEADER %s
 INVALID-FAT-HEADER: macho-invalid-fat-header': truncated or malformed fat file (contains zero architecture types)
 
-RUN: not llvm-objdump --macho --universal-headers %p/Inputs/macho-invalid-fat-arch-size 2>&1 | FileCheck -check-prefix INVALID-FAT-ARCH-SIZE %s
-INVALID-FAT-ARCH-SIZE: macho-invalid-fat-arch-size': truncated or malformed fat file (offset plus size of cputype (7) cpusubtype (3) extends past the end of the file)
+RUN: yaml2obj %p/Inputs/macho-invalid-fat-arch-size.yaml -o - | not llvm-objdump --macho --universal-headers - 2>&1 | FileCheck -check-prefix INVALID-FAT-ARCH-SIZE %s
+INVALID-FAT-ARCH-SIZE: '-': truncated or malformed fat file (offset plus size of cputype (7) cpusubtype (3) extends past the end of the file)
 
 RUN: not llvm-objdump --macho --universal-headers %p/Inputs/macho-invalid-fat-arch-bigalign 2>&1 | FileCheck -check-prefix INVALID-FAT-ARCH-BIGALIGN %s
 INVALID-FAT-ARCH-BIGALIGN: macho-invalid-fat-arch-bigalign': truncated or malformed fat file (align (2^212) too large for cputype (7) cpusubtype (3) (maximum 2^15))