diff --git a/llvm/lib/ObjectYAML/ELFYAML.cpp b/llvm/lib/ObjectYAML/ELFYAML.cpp
--- a/llvm/lib/ObjectYAML/ELFYAML.cpp
+++ b/llvm/lib/ObjectYAML/ELFYAML.cpp
@@ -221,6 +221,7 @@
   ECase(EM_LANAI);
   ECase(EM_BPF);
 #undef ECase
+  IO.enumFallback<Hex16>(Value);
 }
 
 void ScalarEnumerationTraits<ELFYAML::ELF_ELFCLASS>::enumeration(
diff --git a/llvm/test/tools/obj2yaml/elf-emachine.yaml b/llvm/test/tools/obj2yaml/elf-emachine.yaml
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/obj2yaml/elf-emachine.yaml
@@ -0,0 +1,39 @@
+## Check how obj2yaml dumps e_machine field.
+
+## Check it dumps an unknown e_machine as a number.
+
+# RUN: yaml2obj --docnum=1 %s -o %t1
+# RUN: obj2yaml %t1 | FileCheck %s --check-prefix=UNKNOWN
+
+# UNKNOWN:      --- !ELF
+# UNKNOWN-NEXT: FileHeader:
+# UNKNOWN-NEXT:   Class:   ELFCLASS64
+# UNKNOWN-NEXT:   Data:    ELFDATA2MSB
+# UNKNOWN-NEXT:   Type:    ET_REL
+# UNKNOWN-NEXT:   Machine: 0x1234
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2MSB
+  Type:    ET_REL
+  Machine: 0x1234
+
+## Check it dumps a known e_machine value as an enum string.
+
+# RUN: yaml2obj --docnum=2 %s -o %t2
+# RUN: obj2yaml %t2 | FileCheck %s --check-prefix=KNOWN
+
+# KNOWN:      --- !ELF
+# KNOWN-NEXT: FileHeader:
+# KNOWN-NEXT:   Class:   ELFCLASS64
+# KNOWN-NEXT:   Data:    ELFDATA2MSB
+# KNOWN-NEXT:   Type:    ET_REL
+# KNOWN-NEXT:   Machine: EM_NONE
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2MSB
+  Type:    ET_REL
+  Machine: 0
diff --git a/llvm/test/tools/yaml2obj/elf-emachine.yaml b/llvm/test/tools/yaml2obj/elf-emachine.yaml
new file mode 100644
--- /dev/null
+++ b/llvm/test/tools/yaml2obj/elf-emachine.yaml
@@ -0,0 +1,55 @@
+## Test how the Machine YAML field can be used to set the e_machine ELF header field.
+
+## Test we can use an arbitrary value.
+
+# RUN: yaml2obj --docnum=1 %s -o %t1
+# RUN: llvm-readelf %t1 --file-headers | FileCheck %s --check-prefix=UNKNOWN
+
+# UNKNOWN: Machine: 1234
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2MSB
+  Type:    ET_REL
+  Machine: 0x1234
+
+## Test we can't use a number that doesn't fit into 2 bytes.
+
+# RUN: not yaml2obj --docnum=2 %s 2>&1 | FileCheck %s --check-prefix=ERR
+
+# ERR: error: out of range hex16 number
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2MSB
+  Type:    ET_REL
+  Machine: 0x12345
+
+## Test we can use a known named constant.
+
+# RUN: yaml2obj --docnum=3 %s -o %t3
+# RUN: llvm-readelf %t3 --file-headers | FileCheck %s --check-prefix=NONE
+
+# NONE: Machine: None
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2MSB
+  Type:    ET_REL
+  Machine: EM_NONE
+
+## Test we can't use an unknown string constant.
+
+# RUN: not yaml2obj --docnum=4 %s 2>&1 | FileCheck %s --check-prefix=ERR2
+
+# ERR2: error: invalid hex16 number
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2MSB
+  Type:    ET_REL
+  Machine: EM_UNKNOWN_FOO