diff --git a/llvm/lib/MC/MCParser/MasmParser.cpp b/llvm/lib/MC/MCParser/MasmParser.cpp
--- a/llvm/lib/MC/MCParser/MasmParser.cpp
+++ b/llvm/lib/MC/MCParser/MasmParser.cpp
@@ -5957,7 +5957,7 @@
                    IsMacroFunction);
   DEBUG_WITH_TYPE("asm-macros", dbgs() << "Defining new macro:\n";
                   Macro.dump());
-  getContext().defineMacro(Name, std::move(Macro));
+  getContext().defineMacro(Name.lower(), std::move(Macro));
   return false;
 }
 
diff --git a/llvm/test/tools/llvm-ml/macro.asm b/llvm/test/tools/llvm-ml/macro.asm
--- a/llvm/test/tools/llvm-ml/macro.asm
+++ b/llvm/test/tools/llvm-ml/macro.asm
@@ -8,7 +8,7 @@
 
 .code
 
-substitution_macro macro a1:req, a2:=<7>
+SubstitutionMacro macro a1:req, a2:=<7>
   mov eax, a1
   mov eax, a1&
   mov eax, &a1
@@ -27,7 +27,7 @@
 substitution_test_with_default PROC
 ; CHECK-LABEL: substitution_test_with_default:
 
-  substitution_macro 1
+  SubstitutionMacro 1
 ; CHECK: mov eax, 1
 ; CHECK-NEXT: mov eax, 1
 ; CHECK-NEXT: mov eax, 1
@@ -46,7 +46,7 @@
 substitution_test_with_value PROC
 ; CHECK-LABEL: substitution_test_with_value:
 
-  substitution_macro 2, 8
+  SubstitutionMacro 2, 8
 ; CHECK: mov eax, 2
 ; CHECK-NEXT: mov eax, 2
 ; CHECK-NEXT: mov eax, 2
@@ -62,7 +62,45 @@
   ret
 substitution_test_with_value ENDP
 
-ambiguous_substitution_macro MACRO x, y
+substitution_test_lowercase PROC
+; CHECK-LABEL: substitution_test_lowercase:
+
+  substitutionmacro 2, 8
+; CHECK: mov eax, 2
+; CHECK-NEXT: mov eax, 2
+; CHECK-NEXT: mov eax, 2
+; CHECK-NEXT: mov eax, 2
+; CHECK: mov eax, dword ptr [rip + xa1]
+; CHECK-NEXT: mov eax, dword ptr [rip + x2]
+; CHECK-NEXT: mov eax, dword ptr [rip + x2]
+; CHECK: mov eax, 8
+; CHECK-NEXT: mov eax, 8
+; CHECK-NEXT: mov eax, 8
+; CHECK-NEXT: mov eax, 8
+
+  ret
+substitution_test_lowercase ENDP
+
+substitution_test_uppercase PROC
+; CHECK-LABEL: substitution_test_uppercase:
+
+  SUBSTITUTIONMACRO 2, 8
+; CHECK: mov eax, 2
+; CHECK-NEXT: mov eax, 2
+; CHECK-NEXT: mov eax, 2
+; CHECK-NEXT: mov eax, 2
+; CHECK: mov eax, dword ptr [rip + xa1]
+; CHECK-NEXT: mov eax, dword ptr [rip + x2]
+; CHECK-NEXT: mov eax, dword ptr [rip + x2]
+; CHECK: mov eax, 8
+; CHECK-NEXT: mov eax, 8
+; CHECK-NEXT: mov eax, 8
+; CHECK-NEXT: mov eax, 8
+
+  ret
+substitution_test_uppercase ENDP
+
+AmbiguousSubstitutionMacro MACRO x, y
   x&y BYTE 0
 ENDM
 
@@ -70,7 +108,7 @@
 ; CHECK-LABEL: ambiguous_substitution_test:
 
 ; should expand to ab BYTE 0
-  ambiguous_substitution_macro a, b
+  AmbiguousSubstitutionMacro a, b
 
 ; CHECK: ab:
 ; CHECK-NOT: ay:
@@ -78,7 +116,7 @@
 ; CHECK-NOT: xy:
 ambiguous_substitution_test ENDP
 
-ambiguous_substitution_in_string_macro MACRO x, y
+AmbiguousSubstitutionInStringMacro MACRO x, y
   BYTE "x&y"
 ENDM
 
@@ -86,14 +124,14 @@
 ; CHECK-LABEL: ambiguous_substitution_in_string_test:
 
 ; should expand to BYTE "5y"
-  ambiguous_substitution_in_string_macro 5, 7
+  AmbiguousSubstitutionInStringMacro 5, 7
 
 ; CHECK: .byte 53
 ; CHECK-NEXT: .byte 121
 ; CHECK-NOT: .byte
 ambiguous_substitution_in_string_test ENDP
 
-optional_parameter_macro MACRO a1:req, a2
+OptionalParameterMacro MACRO a1:req, a2
   mov eax, a1
 IFNB <a2>
   mov eax, a2
@@ -104,17 +142,17 @@
 optional_parameter_test PROC
 ; CHECK-LABEL: optional_parameter_test:
 
-  optional_parameter_macro 4
+  OptionalParameterMacro 4
 ; CHECK: mov eax, 4
 ; CHECK: ret
 
-  optional_parameter_macro 5, 9
+  OptionalParameterMacro 5, 9
 ; CHECK: mov eax, 5
 ; CHECK: mov eax, 9
 ; CHECK: ret
 optional_parameter_test ENDP
 
-local_symbol_macro MACRO
+LocalSymbolMacro MACRO
   LOCAL a
 a: ret
    jmp a
@@ -123,22 +161,22 @@
 local_symbol_test PROC
 ; CHECK-LABEL: local_symbol_test:
 
-  local_symbol_macro
+  LocalSymbolMacro
 ; CHECK: "??0000":
 ; CHECK-NEXT: ret
 ; CHECK-NEXT: jmp "??0000"
 
-  local_symbol_macro
+  LocalSymbolMacro
 ; CHECK: "??0001":
 ; CHECK-NEXT: ret
 ; CHECK-NEXT: jmp "??0001"
 local_symbol_test ENDP
 
-PURGE ambiguous_substitution_macro, local_symbol_macro,
-      optional_parameter_macro
+PURGE AmbiguousSubstitutionMacro, LocalSymbolMacro,
+      OptionalParameterMacro
 
 ; Redefinition
-local_symbol_macro MACRO
+LocalSymbolMacro MACRO
   LOCAL b
 b: xor eax, eax
    jmp b
@@ -147,7 +185,7 @@
 purge_test PROC
 ; CHECK-LABEL: purge_test:
 
-  local_symbol_macro
+  LocalSymbolMacro
 ; CHECK: "??0002":
 ; CHECK-NEXT: xor eax, eax
 ; CHECK-NEXT: jmp "??0002"