diff --git a/llvm/lib/ObjectYAML/XCOFFEmitter.cpp b/llvm/lib/ObjectYAML/XCOFFEmitter.cpp
--- a/llvm/lib/ObjectYAML/XCOFFEmitter.cpp
+++ b/llvm/lib/ObjectYAML/XCOFFEmitter.cpp
@@ -387,8 +387,17 @@
       }
       W.write<uint32_t>(YamlSym.Value);
     }
-    W.write<int16_t>(
-        YamlSym.SectionName.size() ? SectionIndexMap[YamlSym.SectionName] : 0);
+    if (YamlSym.SectionName.size()) {
+      StringRef SymSecName =
+          StringRef(YamlSym.SectionName.data(), YamlSym.SectionName.size());
+      // If the section name specified in the symbol is not a valid member of
+      // SectionIndexMap, write an invalid index.
+      W.write<int16_t>(SectionIndexMap.find(SymSecName) == SectionIndexMap.end()
+                           ? -3
+                           : SectionIndexMap[YamlSym.SectionName]);
+    } else {
+      W.write<int16_t>(0);
+    }
     W.write<uint16_t>(YamlSym.Type);
     W.write<uint8_t>(YamlSym.StorageClass);
     W.write<uint8_t>(YamlSym.NumberOfAuxEntries);