diff --git a/llvm/test/tools/llvm-objcopy/ELF/binary-input.test b/llvm/test/tools/llvm-objcopy/ELF/binary-input.test
--- a/llvm/test/tools/llvm-objcopy/ELF/binary-input.test
+++ b/llvm/test/tools/llvm-objcopy/ELF/binary-input.test
@@ -118,3 +118,10 @@
 # ALIGN:      Name: .data
 # ALIGN:      AddressAlignment:
 # ALIGN-SAME:                   8{{$}}
+
+## Show that a filename with non-ASCII characters can be handled appropriately.
+## The exact encoding of the non-ASCII character will determine what characters
+## are used, so don't check for them specifically.
+# RUN: cp %t.x-txt %t€.x-txt
+# RUN: llvm-objcopy -I binary -O elf64-x86-64 %t€.x-txt %t3.o
+# RUN: llvm-readobj --sections --symbols %t3.o | FileCheck %s
diff --git a/llvm/tools/llvm-objcopy/ELF/Object.cpp b/llvm/tools/llvm-objcopy/ELF/Object.cpp
--- a/llvm/tools/llvm-objcopy/ELF/Object.cpp
+++ b/llvm/tools/llvm-objcopy/ELF/Object.cpp
@@ -1291,7 +1291,7 @@
 
   std::string SanitizedFilename = MemBuf->getBufferIdentifier().str();
   std::replace_if(std::begin(SanitizedFilename), std::end(SanitizedFilename),
-                  [](char C) { return !isalnum(C); }, '_');
+                  [](char C) { return !isAlnum(C); }, '_');
   Twine Prefix = Twine("_binary_") + SanitizedFilename;
 
   SymTab->addSymbol(Prefix + "_start", STB_GLOBAL, STT_NOTYPE, &DataSection,