diff --git a/lld/ELF/InputSection.cpp b/lld/ELF/InputSection.cpp
--- a/lld/ELF/InputSection.cpp
+++ b/lld/ELF/InputSection.cpp
@@ -347,7 +347,7 @@
 
   // Find a symbol that encloses a given location.
   for (Symbol *b : file->getSymbols())
-    if (auto *d = dyn_cast<Defined>(b))
+    if (auto *d = dyn_cast_or_null<Defined>(b))
       if (d->section == this && d->value <= off && off < d->value + d->size)
         return filename + ":(" + toString(*d) + ")" + archive;
 
diff --git a/lld/test/ELF/invalid/broken-symtab-duplicate-symbol.test b/lld/test/ELF/invalid/broken-symtab-duplicate-symbol.test
new file mode 100644
--- /dev/null
+++ b/lld/test/ELF/invalid/broken-symtab-duplicate-symbol.test
@@ -0,0 +1,28 @@
+# REQUIRES: x86
+## Test that we check nullptr entries in InputFile::symbols (which is supposed to be a
+## non-local symbol list). `local` is a nullptr entry.
+
+# RUN: yaml2obj %s -o %t.o
+# RUN: not ld.lld %t.o %t.o -o /dev/null 2>&1 | FileCheck %s
+# CHECK:      error: duplicate symbol: _start
+# CHECK-NEXT: >>> defined at {{.*}}.o:(.text+0x0)
+# CHECK-NEXT: >>> defined at {{.*}}.o:(.text+0x0)
+
+!ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  OSABI:   ELFOSABI_FREEBSD
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Type:    SHT_PROGBITS
+    Name:    .text
+    Flags:   [ SHF_ALLOC, SHF_EXECINSTR ]
+Symbols:
+  - Name:     _start
+    Section:  .text
+    Binding:  STB_GLOBAL
+  - Name:     local
+    Section:  .text
+    Binding:  STB_LOCAL