Index: test/tools/yaml2obj/elf-comdat-broken.yaml
===================================================================
--- test/tools/yaml2obj/elf-comdat-broken.yaml
+++ test/tools/yaml2obj/elf-comdat-broken.yaml
@@ -0,0 +1,32 @@
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-readobj -sections -elf-section-groups %t | FileCheck %s
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .group
+    Type:            SHT_GROUP
+    Link:            .symtab
+    Info:            foo
+    Members:
+      - SectionOrType:    0xFF
+Symbols:
+  Global:
+    - Name:            foo
+
+## Check we are able to produce SHT_GROUP section with a custom Type (0xFF).
+# CHECK:       Groups {
+# CHECK-NEXT:   Group {
+# CHECK-NEXT:     Name: .group
+# CHECK-NEXT:     Index: 1
+# CHECK-NEXT:     Link: 2
+# CHECK-NEXT:     Info: 1
+# CHECK-NEXT:     Type: COMDAT (0xFF)
+# CHECK-NEXT:     Signature: foo
+# CHECK-NEXT:     Section(s) in group [
+# CHECK-NEXT:     ]
+# CHECK-NEXT:   }
Index: tools/yaml2obj/yaml2elf.cpp
===================================================================
--- tools/yaml2obj/yaml2elf.cpp
+++ tools/yaml2obj/yaml2elf.cpp
@@ -538,10 +538,16 @@
     if (member.sectionNameOrType == "GRP_COMDAT")
       sectionIndex = llvm::ELF::GRP_COMDAT;
     else if (SN2I.lookup(member.sectionNameOrType, sectionIndex)) {
-      WithColor::error() << "Unknown section referenced: '"
-                         << member.sectionNameOrType << "' at YAML section' "
-                         << Section.Name << "\n";
-      return false;
+      // We did not find the section and about to report an error.
+      // As a last resort - try to parse hex value as section index.
+      // This is useful for crafting invalid objects.
+      if (!member.sectionNameOrType.startswith("0x") ||
+          !to_integer(member.sectionNameOrType, sectionIndex)) {
+        WithColor::error() << "Unknown section referenced: '"
+                           << member.sectionNameOrType << "' at YAML section' "
+                           << Section.Name << "\n";
+        return false;
+      }
     }
     SIdx = sectionIndex;
     OS.write((const char *)&SIdx, sizeof(SIdx));