diff --git a/llvm/include/llvm/MC/MCContext.h b/llvm/include/llvm/MC/MCContext.h
--- a/llvm/include/llvm/MC/MCContext.h
+++ b/llvm/include/llvm/MC/MCContext.h
@@ -190,7 +190,8 @@
   SmallString<128> CompilationDir;
 
   /// Prefix replacement map for source file information.
-  std::map<const std::string, const std::string> DebugPrefixMap;
+  std::map<const std::string, const std::string, std::greater<std::string>>
+      DebugPrefixMap;
 
   /// The main file name if passed in explicitly.
   std::string MainFileName;
diff --git a/llvm/test/MC/ELF/debug-prefix-map.s b/llvm/test/MC/ELF/debug-prefix-map.s
--- a/llvm/test/MC/ELF/debug-prefix-map.s
+++ b/llvm/test/MC/ELF/debug-prefix-map.s
@@ -11,9 +11,9 @@
 # RUN: llvm-mc -triple=x86_64 -g -dwarf-version=5 src.s -filetype=obj -o map.5.o -fdebug-prefix-map=%t.foo=src_root
 # RUN: llvm-dwarfdump -v -debug-info -debug-line map.5.o | FileCheck --check-prefix=MAP_V5 %s
 
-# RUN: llvm-mc -triple=x86_64 -g -dwarf-version=4 %t.foo/src.s -filetype=obj -o mapabs.4.o -fdebug-prefix-map=%t.foo=/src_root
+# RUN: llvm-mc -triple=x86_64 -g -dwarf-version=4 %t.foo/src.s -filetype=obj -o mapabs.4.o -fdebug-prefix-map=%t=/broken_root -fdebug-prefix-map=%t.foo=/src_root
 # RUN: llvm-dwarfdump -v -debug-info -debug-line mapabs.4.o | FileCheck --check-prefix=MAPABS_V4 %s
-# RUN: llvm-mc -triple=x86_64 -g -dwarf-version=5 %t.foo/src.s -filetype=obj -o mapabs.5.o -fdebug-prefix-map=%t.foo=/src_root
+# RUN: llvm-mc -triple=x86_64 -g -dwarf-version=5 %t.foo/src.s -filetype=obj -o mapabs.5.o -fdebug-prefix-map=%t=/broken_root -fdebug-prefix-map=%t.foo=/src_root
 # RUN: llvm-dwarfdump -v -debug-info -debug-line mapabs.5.o | FileCheck --check-prefix=MAPABS_V5 %s
 
 f: