Index: ELF/InputFiles.cpp
===================================================================
--- ELF/InputFiles.cpp
+++ ELF/InputFiles.cpp
@@ -931,7 +931,7 @@
   // characters in a filename are replaced with underscore.
   std::string S = "_binary_" + MB.getBufferIdentifier().str();
   for (size_t I = 0; I < S.size(); ++I)
-    if (!isalnum(S[I]))
+    if (!isalnum(static_cast<unsigned char>(S[I])))
       S[I] = '_';
 
   Symtab->addRegular<ELFT>(Saver.save(S + "_start"), STV_DEFAULT, STT_OBJECT,
Index: test/ELF/format-binary-non-ascii.s
===================================================================
--- test/ELF/format-binary-non-ascii.s
+++ test/ELF/format-binary-non-ascii.s
@@ -0,0 +1,15 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t£.o
+
+# RUN: ld.lld -o %t.elf %t£.o --format=binary %t£.o
+# RUN: llvm-readobj -symbols %t.elf | FileCheck %s
+
+# CHECK: Name: _binary_{{[a-zA-Z0-9_]+}}test_ELF_Output_format_binary_non_ascii_s_tmp___o_start
+# CHECK: Name: _binary_{{[a-zA-Z0-9_]+}}test_ELF_Output_format_binary_non_ascii_s_tmp___o_end
+# CHECK: Name: _binary_{{[a-zA-Z0-9_]+}}test_ELF_Output_format_binary_non_ascii_s_tmp___o_size
+
+.text
+.align 4
+.globl _start
+_start:
+    nop