diff --git a/llvm/include/llvm/ObjectYAML/DWARFYAML.h b/llvm/include/llvm/ObjectYAML/DWARFYAML.h
--- a/llvm/include/llvm/ObjectYAML/DWARFYAML.h
+++ b/llvm/include/llvm/ObjectYAML/DWARFYAML.h
@@ -123,7 +123,7 @@
   dwarf::DwarfFormat Format;
   Optional<yaml::Hex64> Length;
   uint16_t Version;
-  uint8_t AddrSize;
+  Optional<uint8_t> AddrSize;
   llvm::dwarf::UnitType Type; // Added in DWARF 5
   yaml::Hex64 AbbrOffset;
   std::vector<Entry> Entries;
diff --git a/llvm/lib/ObjectYAML/DWARFEmitter.cpp b/llvm/lib/ObjectYAML/DWARFEmitter.cpp
--- a/llvm/lib/ObjectYAML/DWARFEmitter.cpp
+++ b/llvm/lib/ObjectYAML/DWARFEmitter.cpp
@@ -382,7 +382,12 @@
 
 Error DWARFYAML::emitDebugInfo(raw_ostream &OS, const DWARFYAML::Data &DI) {
   for (const DWARFYAML::Unit &Unit : DI.CompileUnits) {
-    dwarf::FormParams Params = {Unit.Version, Unit.AddrSize, Unit.Format};
+    uint8_t AddrSize;
+    if (Unit.AddrSize)
+      AddrSize = *Unit.AddrSize;
+    else
+      AddrSize = DI.Is64BitAddrSize ? 8 : 4;
+    dwarf::FormParams Params = {Unit.Version, AddrSize, Unit.Format};
     uint64_t Length = 3; // sizeof(version) + sizeof(address_size)
     Length += Unit.Version >= 5 ? 1 : 0;       // sizeof(unit_type)
     Length += Params.getDwarfOffsetByteSize(); // sizeof(debug_abbrev_offset)
@@ -411,11 +416,11 @@
     writeInteger((uint16_t)Unit.Version, OS, DI.IsLittleEndian);
     if (Unit.Version >= 5) {
       writeInteger((uint8_t)Unit.Type, OS, DI.IsLittleEndian);
-      writeInteger((uint8_t)Unit.AddrSize, OS, DI.IsLittleEndian);
+      writeInteger((uint8_t)AddrSize, OS, DI.IsLittleEndian);
       writeDWARFOffset(Unit.AbbrOffset, Unit.Format, OS, DI.IsLittleEndian);
     } else {
       writeDWARFOffset(Unit.AbbrOffset, Unit.Format, OS, DI.IsLittleEndian);
-      writeInteger((uint8_t)Unit.AddrSize, OS, DI.IsLittleEndian);
+      writeInteger((uint8_t)AddrSize, OS, DI.IsLittleEndian);
     }
 
     OS.write(EntryBuffer.data(), EntryBuffer.size());
diff --git a/llvm/lib/ObjectYAML/DWARFYAML.cpp b/llvm/lib/ObjectYAML/DWARFYAML.cpp
--- a/llvm/lib/ObjectYAML/DWARFYAML.cpp
+++ b/llvm/lib/ObjectYAML/DWARFYAML.cpp
@@ -150,7 +150,7 @@
   if (Unit.Version >= 5)
     IO.mapRequired("UnitType", Unit.Type);
   IO.mapRequired("AbbrOffset", Unit.AbbrOffset);
-  IO.mapRequired("AddrSize", Unit.AddrSize);
+  IO.mapOptional("AddrSize", Unit.AddrSize);
   IO.mapOptional("Entries", Unit.Entries);
 }
 
diff --git a/llvm/test/tools/yaml2obj/ELF/DWARF/debug-info.yaml b/llvm/test/tools/yaml2obj/ELF/DWARF/debug-info.yaml
--- a/llvm/test/tools/yaml2obj/ELF/DWARF/debug-info.yaml
+++ b/llvm/test/tools/yaml2obj/ELF/DWARF/debug-info.yaml
@@ -453,7 +453,6 @@
       Version:    5
       UnitType:   DW_UT_type
       AbbrOffset: 0x1234
-      AddrSize:   4
       Entries:    []
 
 ## e) Test that yaml2obj emits an error message when both the "Content" and the
@@ -482,7 +481,6 @@
       Version:    5
       UnitType:   DW_UT_type
       AbbrOffset: 0x1234
-      AddrSize:   4
       Entries:    []
 
 ## f) Test that all the properties can be overridden by the section header when
@@ -550,7 +548,6 @@
       Version:    5
       UnitType:   DW_UT_type
       AbbrOffset: 0x1234
-      AddrSize:   4
       Entries:
         - AbbrCode: 0
           Values:   []
@@ -568,7 +565,7 @@
 
 --- !ELF
 FileHeader:
-  Class:   ELFCLASS64
+  Class:   ELFCLASS32
   Data:    ELFDATA2LSB
   Type:    ET_EXEC
   Machine: EM_X86_64
@@ -578,7 +575,6 @@
       Version:    5
       UnitType:   DW_UT_type
       AbbrOffset: 0x1234
-      AddrSize:   4
       Entries:    []
 
 ## h) Test that yaml2obj emits values in the DIE according to the abbreviation whose
@@ -604,7 +600,7 @@
 
 --- !ELF
 FileHeader:
-  Class:   ELFCLASS64
+  Class:   ELFCLASS32
   Data:    ELFDATA2LSB
   Type:    ET_EXEC
   Machine: EM_X86_64
@@ -629,7 +625,6 @@
       Version:    5
       UnitType:   DW_UT_type
       AbbrOffset: 0x1234
-      AddrSize:   4
       Entries:
         ## Test that yaml2obj emits values when the abbrev code is specified.
         - AbbrCode: 2
@@ -667,7 +662,6 @@
       Version:    5
       UnitType:   DW_UT_type
       AbbrOffset: 0x1234
-      AddrSize:   4
       Entries:
         - AbbrCode: 1
           Values:
@@ -703,7 +697,6 @@
       Version:    5
       UnitType:   DW_UT_type
       AbbrOffset: 0x1234
-      AddrSize:   8
       Entries:    []
 
 ## DWARFv4 unit header.
@@ -733,7 +726,6 @@
       Length:     0x0c
       Version:    4
       AbbrOffset: 0x1234
-      AddrSize:   8
       Entries:    []
 
 ## k) Test that yaml2obj is able to emit a correct length for compilation units.
@@ -826,7 +818,6 @@
   debug_info:
     - Version:    4
       AbbrOffset: 0x00
-      AddrSize:   0x08
       Entries:
         - AbbrCode: 1
           Values:
@@ -869,8 +860,31 @@
   debug_info:
     - Version:    4
       AbbrOffset: 0x00
-      AddrSize:   0x08
       Entries:
         - AbbrCode: 1
         - AbbrCode: 0
         - AbbrCode: 2
+
+## m) Test that yaml2obj is able to infer the address size from the object file.
+
+# RUN: yaml2obj --docnum=15 -DBITS=64 %s -o %t15.64-bit.o
+# RUN: llvm-readelf --hex-dump=.debug_info %t15.64-bit.o | \
+# RUN:   FileCheck %s --check-prefix=ADDRSIZE -DADDRSIZE=08
+
+#      ADDRSIZE: Hex dump of section '.debug_info':
+# ADDRSIZE-NEXT: 0x00000000 07000000 04000000 0000[[ADDRSIZE]]            ...........
+
+# RUN: yaml2obj --docnum=15 -DBITS=32 %s -o %t15.32-bit.o
+# RUN: llvm-readelf --hex-dump=.debug_info %t15.32-bit.o | \
+# RUN:   FileCheck %s --check-prefix=ADDRSIZE -DADDRSIZE=04
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS[[BITS]]
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_X86_64
+DWARF:
+  debug_info:
+    - Version:    4
+      AbbrOffset: 0x00