diff --git a/lld/COFF/Symbols.h b/lld/COFF/Symbols.h
--- a/lld/COFF/Symbols.h
+++ b/lld/COFF/Symbols.h
@@ -80,6 +80,9 @@
     // is a waste of time.
     if (nameData == nullptr)
       computeName();
+    if (nameData == nullptr)
+      return StringRef{}; // I don't know, if we can be sure, that nameSize is 0
+                          // in this case.
     return StringRef(nameData, nameSize);
   }
 
diff --git a/lld/COFF/Symbols.cpp b/lld/COFF/Symbols.cpp
--- a/lld/COFF/Symbols.cpp
+++ b/lld/COFF/Symbols.cpp
@@ -55,7 +55,9 @@
 void Symbol::computeName() {
   assert(nameData == nullptr &&
          "should only compute the name once for DefinedCOFF symbols");
-  auto *d = cast<DefinedCOFF>(this);
+  auto *d = dyn_cast<DefinedCOFF>(this);
+  if (d == nullptr)
+    return;
   StringRef nameStr =
       check(cast<ObjFile>(d->file)->getCOFFObj()->getSymbolName(d->sym));
   nameData = nameStr.data();
diff --git a/lld/COFF/Writer.cpp b/lld/COFF/Writer.cpp
--- a/lld/COFF/Writer.cpp
+++ b/lld/COFF/Writer.cpp
@@ -396,7 +396,7 @@
   default:
     llvm_unreachable("Unexpected architecture");
   }
-  Defined *d = make<DefinedSynthetic>("", c);
+  Defined *d = make<DefinedSynthetic>("range_extension_thunk", c);
   lastThunk = d;
   return {d, true};
 }
diff --git a/lld/test/COFF/arm-thumb-thunks.s b/lld/test/COFF/arm-thumb-thunks.s
--- a/lld/test/COFF/arm-thumb-thunks.s
+++ b/lld/test/COFF/arm-thumb-thunks.s
@@ -1,6 +1,6 @@
 // REQUIRES: arm
 // RUN: llvm-mc -filetype=obj -triple=thumbv7-windows %s -o %t.obj
-// RUN: lld-link -entry:main -subsystem:console %t.obj -out:%t.exe -verbose 2>&1 | FileCheck -check-prefix=VERBOSE %s
+// RUN: lld-link -entry:main -subsystem:console %t.obj -out:%t.exe -map -verbose 2>&1 | FileCheck -check-prefix=VERBOSE %s
 // RUN: llvm-objdump -d %t.exe --start-address=0x401000 --stop-address=0x401022 | FileCheck --check-prefix=MAIN %s
 // RUN: llvm-objdump -d %t.exe --start-address=0x501022 --stop-address=0x501032 | FileCheck --check-prefix=FUNC1 %s
 // RUN: llvm-objdump -d %t.exe --start-address=0x601032 | FileCheck --check-prefix=FUNC2 %s